metrics: grafana dashboards support multiple cluster (#3389)

[ti-srebot]

cherry-pick #3389 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In pd repo:
git pr https://github.com/tikv/pd/pull/3398

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/pd.git pr/3398:release-4.0-c15cb77a1730

---

What problem does this PR solve?

Many users(come from DBaaS、operator、tiup) monitor multiple TiDB clusters in one Grafana, this PR make Grafana dashboards support multiple clusters and not affect single cluster usage. Cluster variable is hidden by default.

What is changed and how it works?

• add a tidb_cluster label in all expr
• add cluster variable in Grafana templating

How it Works:
load it to your Grafana :))

Single Cluster:
No change

Multiple Cluster:
Construct a label that can uniquely identify the cluster. in tidb_operator, you can use {namespace}-{cluster_name} as your {tidb_cluster} variable.
add this configuration to your prometheus config

relabel_configs:
  - source_labels:
      - namespace
      - name
    separator: "-"
    target_label: tidb_cluster

Check List

Tests

• No code

Code changes

• Has configuration change
• Has HTTP API interfaces change (Don't forget to add the declarative for API)
• Has persistent data change

Side effects

• no effects

Related changes

• metrics: grafana dashboards support multiple clusters pingcap/tidb#22503

Release note

• metrics: grafana dashboards support multiple clusters

[ti-chi-bot]

[REVIEW NOTIFICATION]

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[ti-srebot]

@zjj2wry please accept the invitation then you can push to the cherry-pick pull requests.
https://github.com/ti-srebot/pd/invitations

[nolouch]

@zjj2wry, please resolve the conflict.

[codecov]

Codecov Report

Merging #3398 (74cd43b) into release-4.0 (0812e5b) will decrease coverage by 0.05%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           release-4.0    #3398      +/-   ##
===============================================
- Coverage        74.71%   74.66%   -0.06%     
===============================================
  Files              209      209              
  Lines            19737    19737              
===============================================
- Hits             14747    14736      -11     
- Misses            3650     3665      +15     
+ Partials          1340     1336       -4     

Flag	Coverage Δ
unittests	74.66% <ø> (-0.06%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/errs/errs.go	75.00% <0.00%> (-25.00%)	⬇️
server/region_syncer/client.go	78.74% <0.00%> (-4.73%)	⬇️
pkg/etcdutil/etcdutil.go	72.05% <0.00%> (-4.42%)	⬇️
server/member/leader.go	63.76% <0.00%> (-2.30%)	⬇️
pkg/btree/btree.go	85.30% <0.00%> (-0.97%)	⬇️
server/grpc_service.go	59.07% <0.00%> (-0.81%)	⬇️
client/client.go	69.54% <0.00%> (-0.51%)	⬇️
server/server.go	73.79% <0.00%> (-0.34%)	⬇️
server/cluster/cluster.go	79.45% <0.00%> (+0.49%)	⬆️
server/core/storage.go	68.80% <0.00%> (+0.91%)	⬆️
... and 3 more

---

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[zjj2wry]

/assign

[zjj2wry]

@zjj2wry, please resolve the conflict.

done, ptal

[ti-chi-bot]

@breeswish: /lgtm is only allowed for the reviewers in list.

In response to this:

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[zjj2wry]

@HunDunDM @nolouch PTAL

[HunDunDM]

/merge

[ti-chi-bot]

@HunDunDM: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 74cd43b

[zjj2wry]

/test idc-jenkins-ci-pd/integration-common-test

[zjj2wry]

/run-all-tests

[HunDunDM]

/run-integration-common-test

[zjj2wry]

/run-integration-common-test