br: restore tiflash replica count after PiTR

[YuJuncen]

What problem does this PR solve?

Issue Number: close #37208

Problem Summary:
Currently, we cannot restore the information of TiFlash replicas.

What is changed and how it works?

This PR added some hooks to the PiTR restore process, and would collect the tilfash-related infromation and then generate and execute those DDLs for restoring the TiFlash replicas.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  The script: https://gist.github.com/YuJuncen/4f82d1769a766faa78098923d3e32071
  Checksum matches:

[["310000", "154946.6817939191110397"], ["310000", "154947.6057966217137621"], ["310000", "154820.4573007339340533"]] 
vs 
[["310000", "154946.6817939191110397"], ["310000", "154947.6057966217137621"], ["310000", "154820.4573007339340533"]]; 
equals? = true

TiFlash replica matches:

irb(main):005:0> (SQL.new :downstream).sql 'select * from information_schema.tiflash_replica'
=> [["test", "table4", "215", "1", "", "1", "1", "NORMAL"], ["test", "table3", "216", "1", "", "1", "1", "NORMAL"]]
irb(main):006:0> SQL.new.sql 'select * from information_schema.tiflash_replica'
=> [["test", "table4", "193", "1", "", "1", "1", "NORMAL"], ["test", "table3", "196", "1", "", "1", "1", "NORMAL"]]

• No code

Release note

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

PiTR (Log Backup) can restore TiFlash replica metadata now.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Leavrth
• joccau

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Please follow PR Title Format:

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[ti-chi-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/1ddeb4f68860ff0182178aaf12965ffe8aafad1d

[sre-bot]

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[joccau]

/cc @3pointer @Leavrth PTAL

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@joccau: GitHub didn't allow me to request PR reviews from the following users: PTAL.

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[joccau]

rest LGTM.

[joccau]

LGTM

[joccau]

/merge

[ti-chi-bot]

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

Commit hash: 1ddeb4f

[sre-bot]

TiDB MergeCI notify

✅ Well Done! New fixed [1] after this pr merged.

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/common-test	🔴 failed 1, success 10, total 11	16 min	Existing failure
idc-jenkins-ci-tidb/integration-common-test	✅ all 17 tests passed	17 min	Fixed
idc-jenkins-ci/integration-cdc-test	🟢 all 36 tests passed	35 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	9 min 6 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	7 min 8 sec	Existing passed
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	6 min 40 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	6 min 8 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	3 min 30 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 24 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed