server: Add gRPC interfaces for the new GC APIs.

[MyonKeminta]

What problem does this PR solve?

Issue Number: Ref #8978

What is changed and how does it work?

Add new gRPC API for GC as designed in the refactor task #8978 .
Also adapts the existing GC APIs to the new implementation.

Requires:

• gc: Implement compatibility methods and GetAllKeyspacesGCStates method to GCStateManager #9134
• Add new GC API pingcap/kvproto#1288

Based on #9134 . For diff between this and #9134, see: MyonKeminta/pd@m/gc-state-manager...m/new-gc-grpc-api

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]

Skipping CI for Draft Pull Request.
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[ti-chi-bot]

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[MyonKeminta]

/retest

[codecov]

Codecov Report

Attention: Patch coverage is 1.35135% with 219 lines in your changes missing coverage. Please review.

Project coverage is 75.62%. Comparing base (c22da0f) to head (529e9fc).
Report is 2 commits behind head on master.

❌ Your patch check has failed because the patch coverage (1.35%) is below the target coverage (74.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9189      +/-   ##
==========================================
- Coverage   75.80%   75.62%   -0.19%     
==========================================
  Files         477      477              
  Lines       73532    73897     +365     
==========================================
+ Hits        55743    55884     +141     
- Misses      14304    14527     +223     
- Partials     3485     3486       +1     

Flag	Coverage Δ
unittests	75.62% <1.35%> (-0.19%)	⬇️

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