executor: migrate the the feature about max_user_connections from PingkaiDB to community | tidb-test=pr/2474

[joccau]

What problem does this PR solve?

Issue Number: Close #59203

Problem Summary:

What changed and how does it work?

• TiDB supports max_user_connections to limits the login count when login tidb-server.

Check List

Tests

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

  • I checked and no code files have been changed.

integration test case

• https://github.com/PingCAP-QE/tidb-test/pull/2474

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.

TiDB supports max_user_connections to limits the login count.

[codecov]

Codecov Report

Attention: Patch coverage is 67.78523% with 48 lines in your changes missing coverage. Please review.

Project coverage is 74.6647%. Comparing base (c7ce790) to head (277639e).
Report is 29 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #59197        +/-   ##
================================================
+ Coverage   73.0576%   74.6647%   +1.6071%     
================================================
  Files          1689       1706        +17     
  Lines        466915     470475      +3560     
================================================
+ Hits         341117     351279     +10162     
+ Misses       104849      97275      -7574     
- Partials      20949      21921       +972     

Flag	Coverage Δ
integration	46.0578% <57.0469%> (?)
unit	72.2375% <67.7852%> (-0.0286%)	⬇️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	60.6486% <ø> (+15.3255%)	⬆️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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• pkg/sessionctx/vardef/OWNERS
• pkg/sessionctx/variable/OWNERS

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[joccau]

/test unit-test

[tiprow]

@joccau: The specified target(s) for /test were not found.
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• /test fast_test_tiprow
• /test tidb_parser_test

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/test unit-test

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