Added TiKV RPC CLI and flush log backup tasks in graceful shutdown (#6057)

[ti-chi-bot]

This is an automated cherry-pick of #6057

What problem does this PR solve?

During rolling restart, the lag of log backup may be increased because progress lost of the restarted TiKV.

Closes #6046

What is changed and how does it work?

This added a gRPC Client to TiKV and manually triggered FlushNow when gracefully restarting a TiKV.

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[ti-chi-bot]

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[ti-chi-bot]

@csuzhangxc This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[BornChanger]

@YuJuncen please address the conflict.