br: pick some EBS backup bug fixes to 7.5

[YuJuncen]

What problem does this PR solve?

Issue Number: Ref #52846, #51448, #51957, #52175, #52243, #52049

Problem Summary:
N/A

What changed and how does it work?

This PR picks the following PRs:

• br/operator: fix adapt env for snapshot backup stuck when encountered error #52607
• prepare_snap: establish connection to all stores before pausing admin #51449
• operator: pause scheduler after all connections established #51823
• disk_snap_restore: remove checking store number #51886
• operator: make an infinity retry for connecting to store #52177
• br/operator: fix stuck when terminating #52264
• operator: make gRPC connections synced #52051

Check List

Tests

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

  Because they are cherry-picks.

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

Attention: Patch coverage is 79.31034% with 18 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (release-7.5@61c4bd6). Click here to learn what that means.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #53027   +/-   ##
================================================
  Coverage               ?   72.0361%           
================================================
  Files                  ?       1410           
  Lines                  ?     409833           
  Branches               ?          0           
================================================
  Hits                   ?     295228           
  Misses                 ?      94781           
  Partials               ?      19824           

Flag	Coverage Δ
unit	72.0361% <79.3103%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.5480% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BornChanger, Leavrth

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [Leavrth]
• br/OWNERS [BornChanger,Leavrth]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-06 09:27:29.857108319 +0000 UTC m=+867803.614243888: ☑️ agreed by BornChanger.
• 2024-05-07 04:32:52.078458443 +0000 UTC m=+936525.835594014: ☑️ agreed by Leavrth.