Multi-metrics throttler: adding InnoDB history_list_length metric

[shlomi-noach]

Description

Adding a new and useful throttling metric: InnoDB's history_list_length. This is fetched via

select count as history_len from information_schema.INNODB_METRICS where name = 'trx_rseg_history_len'

The default threshold is 1,000,000,000 (read: high enough)

Related Issue(s)

• RFC: tablet throttler multi-metrics #15624
• Docs: Docs: new MySQL server throttler metrics website#1878

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[codecov]

Codecov Report

Attention: Patch coverage is 28.57143% with 15 lines in your changes missing coverage. Please review.

Project coverage is 67.42%. Comparing base (69b381f) to head (476ffd7).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...tle/base/self_metric_innodb_history_list_length.go	28.57%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17262      +/-   ##
==========================================
+ Coverage   67.40%   67.42%   +0.02%     
==========================================
  Files        1573     1574       +1     
  Lines      253181   253202      +21     
==========================================
+ Hits       170645   170717      +72     
+ Misses      82536    82485      -51     

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[timvaillancourt]

LGTM 👍

FYI: I wondered if this could be gathered using a performance_schema query instead, doesn't look like it

[shlomi-noach]

documentation PR: vitessio/website#1878