grafana: add region heartbeat duration breakdown metrics

[nolouch]

What problem does this PR solve?

Issue Number: Close #7868

What is changed and how does it work?

grafana: add region heartbeat duration breakdown metrics 

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  

Code changes

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

Side effects

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

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HuSharp

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[codecov]

Codecov Report

Merging #7921 (251d379) into master (6ee25f9) will decrease coverage by 0.10%.
The diff coverage is n/a.

❗ Current head 251d379 differs from pull request most recent head f3c6fb3. Consider uploading reports for the commit f3c6fb3 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7921      +/-   ##
==========================================
- Coverage   73.57%   73.48%   -0.10%     
==========================================
  Files         436      436              
  Lines       48351    48342       -9     
==========================================
- Hits        35574    35522      -52     
- Misses       9721     9763      +42     
- Partials     3056     3057       +1     

Flag	Coverage Δ
unittests	73.48% <ø> (-0.10%)	⬇️

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[nolouch]

/merge

[ti-chi-bot]

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

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 251d379

[ti-chi-bot]

@nolouch: Your PR was out of date, I have automatically updated it for you.

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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