resource_manager: add metrics to show resource group configuration

[nolouch]

What problem does this PR solve?

Issue Number: Close https://github.com/tikv/pd/issues/8444

What is changed and how does it work?

Check List

Tests

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

Release note

None.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.50%. Comparing base (ff71512) to head (f08d4de). Report is 58 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8478      +/-   ##
==========================================
+ Coverage   77.46%   77.50%   +0.04%     
==========================================
  Files         472      472              
  Lines       61795    61800       +5     
==========================================
+ Hits        47867    47901      +34     
+ Misses      10371    10330      -41     
- Partials     3557     3569      +12     

Flag	Coverage Δ
unittests	77.50% <80.00%> (+0.04%)	:arrow_up:

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

[nolouch]

PTAL @JmPotato @HuSharp

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files:

• ~~OWNERS~~ [HuSharp,JmPotato]

Approvers can indicate their approval by writing /approve in a comment Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-08-06 07:55:54.798519546 +0000 UTC m=+338684.665618632: :ballot_box_with_check: agreed by JmPotato.
• 2024-08-08 06:29:35.721695822 +0000 UTC m=+506305.588794907: :ballot_box_with_check: agreed by HuSharp.

[nolouch]

/run-cherry-picker

[nolouch]

/run-cherry-picker

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #8638.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #8639.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #8640.