resourcemanager: return resource-group priority in OnRequestWait (#7378)

[ti-chi-bot]

This is an automated cherry-pick of #7378

What problem does this PR solve?

Issue Number: close #7379, ref tikv/tikv#15994

What is changed and how does it work?

return resource-group priority in OnRequestWait so client-go can set the resource-group priority to kv request.

Check List

Tests

• Unit test

Code changes

Side effects

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]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• CabinfeverB
• nolouch

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[codecov]

Codecov Report

Merging #7383 (ffc3fc5) into release-7.5 (d0a17ca) will increase coverage by 0.03%.
The diff coverage is 80.00%.

❗ Current head ffc3fc5 differs from pull request most recent head 4255a28. Consider uploading reports for the commit 4255a28 to get more accurate results

Additional details and impacted files

@@               Coverage Diff               @@
##           release-7.5    #7383      +/-   ##
===============================================
+ Coverage        74.61%   74.64%   +0.03%     
===============================================
  Files              442      442              
  Lines            47822    47822              
===============================================
+ Hits             35682    35699      +17     
+ Misses            8985     8969      -16     
+ Partials          3155     3154       -1     

Flag	Coverage Δ
unittests	74.64% <80.00%> (+0.03%)	⬆️

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[nolouch]

/merge

[ti-chi-bot]

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[ti-chi-bot]

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

Commit hash: 4255a28