log_backup: added more info for slow regions in log backup advancer

[YuJuncen]

What problem does this PR solve?

Issue Number: close #51046

Problem Summary:
It is painful for debugging slow regions in log backup for now. Exactly when there are many TiKV nodes in the cluster: we only have a range but know nothing about which region this key belongs to.
Also we must pick the TiDB log (which isn't always easily accessible.) for such information.

What changed and how does it work?

This PR added two new series to the log backup advancer, which presents the current slowest region's leader location and its region id.
Also we will append more detailed hints about the slowest range.

Check List

Tests

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

  • I checked and no code files have been changed.

Release note

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

None

[tiprow]

Hi @YuJuncen. Thanks for your PR.

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[codecov]

Codecov Report

Merging #51137 (1771bb7) into master (a465300) will decrease coverage by 16.1352%.
Report is 8 commits behind head on master.
The diff coverage is 67.5000%.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #51137         +/-   ##
=================================================
- Coverage   70.6268%   54.4916%   -16.1352%     
=================================================
  Files          1467       1576        +109     
  Lines        434809     603562     +168753     
=================================================
+ Hits         307092     328891      +21799     
- Misses       108517     252105     +143588     
- Partials      19200      22566       +3366     

Flag	Coverage Δ
integration	36.6107% <2.5000%> (?)
unit	70.4018% <67.5000%> (-0.0301%)	⬇️

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

Components	Coverage Δ
dumpling	53.9957% <ø> (-0.0313%)	⬇️
parser	∅ <ø> (∅)
br	51.1621% <67.5000%> (+5.2936%)	⬆️

[Leavrth]

how about using <=?

[YuJuncen]

Given the scale of TSO is millisecond, I guess the difference is minor between <= and <? 🤔

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-19 07:48:54.818527376 +0000 UTC m=+257023.566150522: ☑️ agreed by Leavrth.
• 2024-02-20 02:24:41.665973441 +0000 UTC m=+323970.413596537: ☑️ agreed by BornChanger.

[BornChanger]

/retest

[tiprow]

@BornChanger: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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[YuJuncen]

/run-cherry-picker

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #51173.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #51174.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #51175.