Add alternative usages for the REST APIs and configurations that contain "master" terminology

[tlfeng]

Is your feature request related to a problem? Please describe.
Replace "master" terminology in REST APIs and configurations, where the backwards compatibility will be impacted.

A part of #472

Describe the solution you'd like

1. Replace the old usages that having the word "master" with "cluster manager" in REST APIs and configurations, then create duplicate usages with the original name for backwards compatibility (including fallback logic to fallback to settings with the new name).
2. Add tests to check both old and new usages of the REST APIs and configurations.
3. Add proper deprecation notice to the old usages.

Sub-tasks:

Setting name:

• Deprecate setting cluster.initial_master_nodes and introduce the alternative setting cluster.initial_cluster_manager_nodes. (PR: Deprecate setting 'cluster.initial_master_nodes' and introduce the alternative setting 'cluster.initial_cluster_manager_nodes' #2463)
• Deprecate setting cluster.service.slow_master_task_logging_threshold and introduce the alternative setting .cluster.service.slow_cluster_manager_task_logging_threshold. (PR: Deprecate setting 'cluster.service.slow_master_task_logging_threshold' and introduce the alternative setting 'cluster.service.slow_cluster_manager_task_logging_threshold' #2451)
• Deprecate setting cluster.no_master_block and introduce the alternative setting cluster.no_cluster_manager_block. (PR: Deprecate setting 'cluster.no_master_block' and introduce the alternative setting 'cluster.no_cluster_manager_block' #2453)

Setting value:

• Add a new node role cluster_manager that has the same functionality with master in the node setting node.roles: [ master ] (PR: Add a new node role 'cluster_manager' as the alternative for 'master' role and deprecate 'master' role #2424)

REST API endpoint:

• Add a new REST API GET _cat/cluster_manager as the replacement of GET _cat/master (PR: Add a new REST API endpoint 'GET _cat/cluster_manager' as the replacement of 'GET _cat/master' #2404)

REST API path parameter:

• Make the "node filters" <node_id> used as the request parameter for some REST API accept values with "cluster_manager" as an alternative to "master" (PR: Add a new node role 'cluster_manager' as the alternative for 'master' role and deprecate 'master' role #2424)

REST API request parameter name:

• Add a new request parameter "cluster_manager_timeout" in the REST APIs that accept "master_timeout" parameter, and deprecate "master_timeout" (Issue: Add a new request parameter "cluster_manager_timeout" in the REST APIs that accept "master_timeout" parameter, and deprecate "master_timeout" #2511)
• • CAT Nodes API - this will be a sample (PR: Add request parameter 'cluster_manager_timeout' as the alternative for 'master_timeout', and deprecate 'master_timeout' - in CAT Nodes API #2435)
• See below for the full list of impacted REST APIs

REST API request parameter value:

• Make the request parameter "metric" in "Cluster reroute" and "Cluster state" API accept value "cluster_manager_node" as an alternative to "master_node" (PR: Add 'cluster_manager_node' into ClusterState Metric as an alternative to 'master_node' #2415)

REST API response field:

• Add a new field "discovered_cluster_manager" in the response of GET _cluster/health API that shows identical value of field "discovered_master" (PR: Add a field 'discovered_cluster_manager' in 'GET Cluster Health' API that shows identical value with field 'discovered_master' #2437)
• Replace the "discovered_master" with "discovered_cluster_manager" in the response of GET _cat/health API (PR: Replace 'discovered_master' with 'discovered_cluster_manager' in 'GET Cat Health' API #2438)
• Replace the "master" with "cluster_manager" in the response of GET _cat/nodes API (PR: Replace 'master' with 'cluster_manager' in 'GET Cat Nodes' API #2441)

Describe alternatives you've considered
None.

Additional context
Location that contains the exclusionary term and will impact the compatibility when changed:
Setting names
1 Discovery and cluster formation settings
cluster.initial_master_nodes (static)
cluster.no_master_block (dynamic)
discovery.zen.no_master_block
discovery.zen.minimum_master_nodes
discovery.zen.master_election.*
Note: discovery.zen.* settings are already deprecated in Elasticsearch 7.0, but code remains to be removed. Update: they have been removed in OpenSearch 2.0 by the commit 4db97aa

2 Local gateway settings
gateway.expected_master_nodes
gateway.recover_after_master_nodes
Note: the above 2 settings are already deprecated in Elasticsearch 7.7, but code remains to be removed.

3 Miscellaneous
cluster.service.slow_master_task_logging_threshold (dynamic)
Code: https://github.com/opensearch-project/OpenSearch/blob/1.0.0/server/src/main/java/org/opensearch/cluster/service/MasterService.java#L90

Setting values
1 Node roles
node.roles: [ master ] (static)

REST API endpoints
1 cat master
GET _cat/master

REST API path parameters
1 "node filters" used in some cluster-level APIs. The APIs are usually in the format: GET /_nodes/<node_id>, where <node_id> can be set as _master or master:true or master:false to filter the master nodes.
Nodes Info API API - GET /_nodes/<node_id>
Nodes stats API - GET /_nodes/<node_id>/stats , GET/_nodes/<node_id>/stats/<metric> , GET /_nodes/<node_id>/stats/<metric>/<index_metric>
Nodes feature usage API - GET /_nodes/<node_id>/usage , GET /_nodes/<node_id>/usage/<metric>
Nodes hot threads API - GET /_nodes/<node_id>/hot_threads
Nodes reload secure settings API - POST /_nodes/<node_id>/reload_secure_settings
Task management API - GET _tasks?nodes=<node_id>

REST API request parameter names
1 master_timeout (used in multiple APIs)

• In CAT API:
  CAT Allocation API https://opensearch.org/docs/opensearch/rest-api/cat/cat-allocation/
  CAT Indices API https://opensearch.org/docs/opensearch/rest-api/cat/cat-indices/
  CAT Master API https://opensearch.org/docs/opensearch/rest-api/cat/cat-master/
  CAT Nodeattrs API https://opensearch.org/docs/opensearch/rest-api/cat/cat-nodeattrs/
  CAT Nodes API https://opensearch.org/docs/latest/opensearch/rest-api/cat/cat-nodes/
  CAT Pending tasks API https://opensearch.org/docs/opensearch/rest-api/cat/cat-pending-tasks/
  CAT Plugins API https://opensearch.org/docs/opensearch/rest-api/cat/cat-plugins/
  CAT Repositories API https://opensearch.org/docs/opensearch/rest-api/cat/cat-repositories/
  CAT Shards API https://opensearch.org/docs/opensearch/rest-api/cat/cat-shards/
  CAT Snapshots API https://opensearch.org/docs/opensearch/rest-api/cat/cat-snapshots/
  CAT Templates API https://opensearch.org/docs/opensearch/rest-api/cat/cat-templates/
  CAT Thread pool API https://opensearch.org/docs/opensearch/rest-api/cat/cat-thread-pool/
  CAT Segment API https://opensearch.org/docs/latest/opensearch/rest-api/cat/cat-segments/
• In Cluster API:
  Cluster health API https://opensearch.org/docs/opensearch/rest-api/cluster-health/
  Cluster reroute API - POST /_cluster/reroute
  Cluster state API - GET /_cluster/state/<metrics>/<target>
  Cluster get settings API https://opensearch.org/docs/latest/opensearch/rest-api/cluster-settings/
  Cluster update settings API https://opensearch.org/docs/latest/opensearch/rest-api/cluster-settings/
  Pending cluster tasks API - GET /_cluster/pending_tasks
• In Index API:
  Index management:
  Create index API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/create-index/
  Delete index API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/delete-index/
  Get index API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/get-index/
  Open index API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/open-index/
  Close index API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/close-index/
  Clone index API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/clone/
  Shrink index API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/shrink-index/
  Split index API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/split/
  Rollover index API POST /<rollover-target>/_rollover/<target-index>
  Alias management:
  Add index alias API https://opensearch.org/docs/latest/opensearch/rest-api/alias/
  Delete index alias API DELETE /<index>/_alias/<alias>
  Mapping management:
  Get mapping API
  Put mapping API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/put-mapping/
  Index settings:
  Get Index Settings API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/get-settings/
  Update index settings API https://opensearch.org/docs/latest/opensearch/rest-api/index-apis/update-settings/
  Index templates:
  Get (Legacy) Index Template API GET /_template/<index-template>
  Delete (Legacy) Index Template API DELETE /_template/<index-template>
  Put (Legacy) Index Template API PUT /_template/<index-template>
  Get (Composable) Index Template API GET /_index_template/<index-template>
  Delete (Composable) Index Template API
  Put (Composable) Index Template API
  Get Component Template API GET /_component_template/<index-template>
  Delete Component Template API
  Put Component Template API
  Simulate index API POST /_index_template/_simulate_index/{name}
  Simulate index template API POST /_index_template/_simulate
  Dangling indices:
  Delete Dangling Index API
  Import Dangling Index API POST /_dangling/<index-uuid>
  Other:
  Add index block API PUT /<index>/_block/<block>
• In Snapshot API:
  Put snapshot repository API PUT /_snapshot/<repository>, POST /_snapshot/<repository>
  Get snapshot repository API
  Delete snapshot repository API
  Clean up snapshot repository API POST /_snapshot/<repository>/_cleanup
  Verify snapshot repository API POST /_snapshot/<repository>/_verify
  Create snapshot API
  Get snapshot API
  Delete snapshot API
  Restore snapshot API POST /_snapshot/<repository>/<snapshot>/_restore
  Clone snapshot API
  Get snapshot status API GET _snapshot/<repository>/<snapshot>/_status
• In Ingest API:
  Put pipeline API https://opensearch.org/docs/latest/opensearch/rest-api/ingest-apis/create-update-ingest/
  Get pipeline API https://opensearch.org/docs/latest/opensearch/rest-api/ingest-apis/get-ingest/
  Delete pipeline API https://opensearch.org/docs/latest/opensearch/rest-api/ingest-apis/delete-ingest/
• In Script API:
  Get stored script API GET _scripts/<script-id>
  Put stored script API
  Delete stored script API

REST API request parameter values
1 metric=master_node
Cluster reroute API - POST /_cluster/reroute
Cluster state API - GET /_cluster/state/<metrics>/<target>

REST API response fields
1 discovered_master
Response of GET _cluster/health
doc: https://opensearch.org/docs/latest/opensearch/rest-api/cluster-health/#response
code: https://github.com/opensearch-project/OpenSearch/blob/1.1.0/server/src/main/java/org/opensearch/action/admin/cluster/health/ClusterHealthResponse.java#L69
Response of GET _cat/health (in the header of table)
doc: https://opensearch.org/docs/latest/opensearch/rest-api/cat/cat-health/#response
code: https://github.com/opensearch-project/OpenSearch/blob/1.2.4/server/src/main/java/org/opensearch/rest/action/cat/RestHealthAction.java#L91

2 cat nodes
Response of GET _cat/nodes

The guide for plugins can be a reference: https://github.com/opensearch-project/opensearch-plugins/blob/ece53bf9e93403272726eb6087ed98f9c821502b/UPGRADING.md#settings

[tlfeng]

Pending tasks apart from the above PRs:

• Update the documentation link for API cat/_cluster_manager.
  Source: Add a new REST API endpoint 'GET _cat/cluster_manager' as the replacement of 'GET _cat/master' #2404 (comment)
  Note: document update requested by [FEATURE] Change the "master" nomenclature documentation-website#450

[tlfeng]

All required changes for version 2.0 are completed.
All the REST APIs and Settings which contain "master" terminology have got inclusive alternatives.
All the non-inclusive REST APIs and Settings are deprecated in version 2.0, except REST API request parameter master_timeout. (See issue #2928 for the timeline of the deprecation for master_timeout)