grpc_service: add `ManuallyChangePeer` and `ManuallyChangeMultiPeers`.

[LykxSassinator]

What problem does this PR solve?

Issue Number: Ref https://github.com/tikv/tikv/issues/15292 proto: https://github.com/pingcap/kvproto/pull/1250

What is changed and how does it work?

Make `grpc_service` support manually add / remove peers by `ManuallyChangePeer` and `ManuallyChangeMultiPeers`.

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

Add extra apis `ManuallyChangePeer` and `ManuallyChangeMultiPeers` for `grpc_service` to support manually add / remove peers.

[ti-chi-bot[bot]]

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[LykxSassinator]

/cc @nolouch

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ti-chi-bot[bot]]

[FORMAT CHECKER NOTIFICATION]

Notice: To remove the do-not-merge/needs-linked-issue label, please provide the linked issue number on one line in the PR body, for example: Issue Number: close #123 or Issue Number: ref #456, multiple issues should use full syntax for each issue and be separated by a comma, like: Issue Number: close #123, ref #456.

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[LykxSassinator]

This pr can be closed as this RPC is not necessary.