[FEATURE] Add support for inclusive naming

[wbeckler]

Add support for inclusive naming by deprecating the master nomenclature.

See meta issue opensearch-project/opensearch-clients#16 for details.

[Yury-Fridlyand]

@wbeckler,
This is already done in scope of #51.

• All master references replaced by cluster_manager
  except
  master references in API (it is marked as obsolete, but not removed yet) and in comments to these API:
  • master node renamed to cluster_manager (actually duplicated for BWC with OpenSearch 1.x)
  • master_timeout field renamed to cluster_manager_timeout (duplicated too)
  • masterEligible duplicated by clusterManagerEligible (not an OpenSearch API, but might be in use by customer applications)
• Fortunately, no blacklist/whitelist references in the client code/API, nothing to do there.

Please, check if something is missed and report here. Otherwise we can close this ticket once #51 merged.

[harshavamsi]

@wbeckler @Yury-Fridlyand can we close this?