br: support reset_tiflash after ebs restoration (#40124)

[fengou1]

What problem does this PR solve?

Issue Number: close #40208

Problem Summary: resettle tiflash replica after ebs restoration. This PR associate with pingcap/tidb-operator#4812.

What is changed and how it works?

Check List

Tests

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

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Leavrth
• joccau

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[fengou1]

/test unit-test

[joccau]

LGTM

[joccau]

/merge

[ti-chi-bot]

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

Commit hash: cd1a520