log_backup: added more info for slow regions in log backup advancer (#51137)

[ti-chi-bot]

This is an automated cherry-pick of #51137

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

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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Needs approval from an approver in each of these files:

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

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-20 04:25:09.260421045 +0000 UTC m=+331198.008044156: ☑️ agreed by YuJuncen.
• 2024-02-20 04:32:26.545361742 +0000 UTC m=+331635.292984852: ☑️ agreed by Leavrth.

[BornChanger]

/retest

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.5@245dd62). Click here to learn what that means.
The diff coverage is 75.4717%.

Additional details and impacted files

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Flag	Coverage Δ
unit	71.9975% <75.4717%> (?)

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

Components	Coverage Δ
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parser	∅ <0.0000%> (?)
br	53.2860% <0.0000%> (?)

[BornChanger]

/retest

[wuhuizuo]

/hold
wait for merging of #51164

[wuhuizuo]

/unhold