statistics: record last gc ts to avoid huge read on stats table (#46138)

[ti-chi-bot]

This is an automated cherry-pick of #46138

What problem does this PR solve?

Issue Number: close #45966, close #31778

Problem Summary:

The previous GCStats will read nearly all the stats into the memory

What is changed and how it works?

This pull tries to limit its influence.

Check List

Tests

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

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 61.97183% with 27 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-6.5@ce5bdfe). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #55381   +/-   ##
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  Coverage               ?   73.6270%           
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  Files                  ?       1096           
  Lines                  ?     352414           
  Branches               ?          0           
================================================
  Hits                   ?     259472           
  Misses                 ?      76253           
  Partials               ?      16689           

[ti-chi-bot]

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, winoros

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-24 02:39:12.104316902 +0000 UTC m=+578747.238767015: ☑️ agreed by hawkingrei.
• 2024-08-25 23:44:59.686521273 +0000 UTC m=+741094.820971395: ☑️ agreed by winoros.