resourcemanager: return resource-group priority in OnRequestWait

[glorv]

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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[glorv]

@nolouch @CabinfeverB PTAL

[codecov]

Codecov Report

Merging #7378 (5b74603) into master (0ebf4b2) will increase coverage by 0.08%.
Report is 1 commits behind head on master.
The diff coverage is 80.00%.

❗ Current head 5b74603 differs from pull request most recent head 0064eac. Consider uploading reports for the commit 0064eac to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7378      +/-   ##
==========================================
+ Coverage   74.18%   74.27%   +0.08%     
==========================================
  Files         451      451              
  Lines       48877    48877              
==========================================
+ Hits        36261    36302      +41     
+ Misses       9390     9350      -40     
+ Partials     3226     3225       -1     

Flag	Coverage Δ
unittests	74.27% <80.00%> (+0.08%)	⬆️

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[CabinfeverB]

/merge

[ti-chi-bot]

@CabinfeverB: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 5b74603

[ti-chi-bot]

@glorv: Your PR was out of date, I have automatically updated it for you.

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #7383.