*: fix deletion of region stats metrics after resign (#6367)

[ti-chi-bot]

This is an automated cherry-pick of #6367

What problem does this PR solve?

Issue Number: Close #6366

What is changed and how does it work?

https://github.com/prometheus/client_golang/blob/d7896d4bd082b17e525c29055d79cc29484aa9cb/prometheus/vec.go#L125 doesn't reset the gauge in this metrics vec, instead, it deletes them all.

*: fix deletion of region stats metrics after resign

Check List

Tests

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

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:

• rleungx

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.05 ⚠️

Comparison is base (2695008) 75.03% compared to head (658c10d) 74.99%.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-7.1    #6368      +/-   ##
===============================================
- Coverage        75.03%   74.99%   -0.05%     
===============================================
  Files              408      408              
  Lines            40468    40481      +13     
===============================================
- Hits             30367    30359       -8     
- Misses            7441     7460      +19     
- Partials          2660     2662       +2     

Flag	Coverage Δ
unittests	74.99% <100.00%> (-0.05%)	⬇️

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

Impacted Files	Coverage Δ
pkg/statistics/region_collection.go	97.67% <100.00%> (+0.14%)	⬆️
pkg/storage/endpoint/tso.go	83.87% <100.00%> (-6.46%)	⬇️

... and 33 files with indirect coverage changes

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[rleungx]

/merge

[ti-chi-bot]

@rleungx: 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: 658c10d