check: remove orphan peer only when the peers is greater than the rule count (#7581)

[ti-chi-bot]

This is an automated cherry-pick of #7581

What problem does this PR solve?

Issue Number: Close #7584

What is changed and how does it work?

The healthy orphan peer should be the last one to be removed only if there are extra peers to keep the high availablility.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  https://tcms.pingcap.net/dashboard/executions/plan/5251069

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch

Release note

The healthy orphan peer should be the last one to be removed only if there are extra peers to keep the high availablility.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• bufferflies
• rleungx

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[codecov]

Codecov Report

Attention: 28 lines in your changes are missing coverage. Please review.

Comparison is base (c5d6f3f) 74.85% compared to head (15f919a) 74.75%.
Report is 3 commits behind head on release-7.1.

Files	Patch %	Lines
...s/pd-ctl/pdctl/command/resource_manager_command.go	70.00%	10 Missing and 5 partials ⚠️
client/resource_group/controller/controller.go	75.00%	3 Missing and 2 partials ⚠️
pkg/mcs/resource_manager/server/manager.go	66.66%	5 Missing ⚠️
pkg/mcs/resource_manager/server/resource_group.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           release-7.1    #7592      +/-   ##
===============================================
- Coverage        74.85%   74.75%   -0.10%     
===============================================
  Files              410      411       +1     
  Lines            41544    41632      +88     
===============================================
+ Hits             31099    31124      +25     
- Misses            7709     7758      +49     
- Partials          2736     2750      +14     

Flag	Coverage Δ
unittests	74.75% <75.00%> (-0.10%)	⬇️

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[bufferflies]

/merge

[ti-chi-bot]

@bufferflies: 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: 15f919a