br/stream: allow pitr to create oversized indices (#58433)

[ti-chi-bot]

This is an automated cherry-pick of #58433

What problem does this PR solve?

Issue Number: close #58430

Problem Summary:
During restoring, the internal config of BR wasn't updated.
It may reject all indices longer than the default config (3072) though the target cluster modified this config.

What changed and how does it work?

This updates the TiDB config of the BR internal TiDB instance during restoring incremental data.

Check List

Tests

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

  • I checked and no code files have been changed.

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.

Fixed a bug that caused cannot restore index created during log backup if it is longer than `3072`.

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/unit-test	7adf279	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	7adf279	link	true	/test check-dev2
idc-jenkins-ci-tidb/check_dev	7adf279	link	true	/test check-dev
idc-jenkins-ci-tidb/build	7adf279	link	true	/test build
idc-jenkins-ci-tidb/mysql-test	7adf279	link	true	/test mysql-test

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