metrics: support multi-k8s in grafana dashboards (#4658)

[ti-chi-bot]

This is an automated cherry-pick of #4658

Signed-off-by: just1900 legendj228@gmail.com

What problem does this PR solve?

K8s community and organizations are increasingly deploying multiple Kubernetes clusters to improve availability, isolation and scalability. Since TiDB Operator have support deploying tidb across-kubernetes, this PR will address the multi-k8s issue without affecting existing single-cluster use case.

Issue Number: close #4665

What is changed and how it works?

What's Changed:

• add a k8s_cluster label in all expr
• add k8s_cluster variable in Grafana templating

How it works:

• For users with single-k8s, nothing need to be changed, just use it as before.
• For users with multi-k8s:
  • first add kubernetes label to identify k8s cluster in your prometheus' external_labels.
  • set field "hide" to '0' to show variables in grafana via sed -i s/"hide": 2/"hide": 0/g <path/to/dashboard.json>
  • load it to grafana

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to update key monitor metrics in both TiCDC document and official document

Release note

metrics: support multi-k8s in grafana dashboards

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (release-5.0@21d6d6f). Click here to learn what that means.
The diff coverage is n/a.

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