client: introduce RPCClient

[CabinfeverB]

What problem does this PR solve?

Issue Number: ref #8047

What is changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

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:

• nolouch

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[codecov]

Codecov Report

Merging #8048 (b165d37) into master (f0eb74b) will increase coverage by 0.07%.
Report is 1 commits behind head on master.
The diff coverage is n/a.

❗ Current head b165d37 differs from pull request most recent head 39c622b. Consider uploading reports for the commit 39c622b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8048      +/-   ##
==========================================
+ Coverage   77.24%   77.32%   +0.07%     
==========================================
  Files         468      468              
  Lines       60879    60867      -12     
==========================================
+ Hits        47024    47063      +39     
+ Misses      10304    10264      -40     
+ Partials     3551     3540      -11     

Flag	Coverage Δ
unittests	77.32% <ø> (+0.07%)	⬆️

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[nolouch]

/merge

[ti-chi-bot]

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

/run-all-tests

You only need to trigger /merge once, and 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]

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

Commit hash: b165d37

[ti-chi-bot]

@CabinfeverB: Your PR was out of date, I have automatically updated it for you.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

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.