rg/controller: optimize the fallback mechanism of the controller

[JmPotato]

What problem does this PR solve?

Issue Number: close #8388.

What is changed and how does it work?

This PR implements a more robust fallback method, which uses an independent default group controller for each tombstone group.

Check List

Tests

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

Support multiple dynamic changes:

No interruption even after the GC cleanup:

Release note

None.

[nolouch]

rest lgtm

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 18 lines in your changes missing coverage. Please review.

Project coverage is 77.21%. Comparing base (cbba49a) to head (916354f).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8402      +/-   ##
==========================================
- Coverage   77.24%   77.21%   -0.04%     
==========================================
  Files         471      471              
  Lines       61700    61728      +28     
==========================================
+ Hits        47662    47664       +2     
- Misses      10463    10477      +14     
- Partials     3575     3587      +12     

Flag	Coverage Δ
unittests	77.21% <66.66%> (-0.04%)	⬇️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: HuSharp, nolouch

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Needs approval from an approver in each of these files:

• OWNERS [HuSharp,nolouch]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-07-16 14:29:16.696312092 +0000 UTC m=+364178.687253554: ☑️ agreed by HuSharp.
• 2024-07-17 05:29:40.970140799 +0000 UTC m=+418202.961082268: ☑️ agreed by nolouch.