mcs: add region stats to scheduling cluster

[rleungx]

What problem does this PR solve?

Issue Number: Ref #5839.

What is changed and how does it work?

The region heartbeat handling relies on the region stats and coordinator.

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JmPotato
• lhy1024

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[codecov]

Codecov Report

Merging #6985 (f179e8e) into master (50368e5) will increase coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head f179e8e differs from pull request most recent head e46e90a. Consider uploading reports for the commit e46e90a to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6985      +/-   ##
==========================================
+ Coverage   74.18%   74.23%   +0.04%     
==========================================
  Files         433      433              
  Lines       46133    46082      -51     
==========================================
- Hits        34225    34207      -18     
+ Misses       8887     8862      -25     
+ Partials     3021     3013       -8     

Flag	Coverage Δ
unittests	74.23% <100.00%> (+0.04%)	⬆️

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[rleungx]

@JmPotato PTAL

[JmPotato]

/merge

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: e46e90a