br: use merge-schedule-limit to pause merge (#47576)

[ti-chi-bot]

This is an automated cherry-pick of #47576

What problem does this PR solve?

Issue Number: ref tikv/pd#7148

Problem Summary:
max-merge-region-keys is not a stable arguments.
merge-schedule-limit is more stable to control the merge operator.

What is changed and how it works?

use merge-schedule-limit instead of other arguments to control the merge operator during restore.

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.

None

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-6.5@b7f909c). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #48247   +/-   ##
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  Coverage               ?   74.0461%           
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  Files                  ?       1086           
  Lines                  ?     352661           
  Branches               ?          0           
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  Hits                   ?     261132           
  Misses                 ?      75202           
  Partials               ?      16327           

[ti-chi-bot]

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 3pointer, CabinfeverB, nolouch

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• OWNERS [3pointer]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-22 07:54:22.918905316 +0000 UTC m=+390891.584131504: ☑️ agreed by 3pointer.
• 2023-11-22 08:00:23.979095383 +0000 UTC m=+391252.644321579: ☑️ agreed by nolouch.

[CabinfeverB]

/retest-required

[hawkingrei]

/retest