*: add sql variable @@tidb_accelerate_user_creation_update

[tiancaiamao]

What problem does this PR solve?

Issue Number: ref #55563

Problem Summary:

What changed and how does it work?

Add a switch to control the behavior.
If @@tidb_accelerate_user_creation_update = off, use the old behavior, i.e. load all the user data
If @@tidb_accelerate_user_creation_update = on, only load the active user

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.

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

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[codecov]

Codecov Report

Attention: Patch coverage is 73.52941% with 9 lines in your changes missing coverage. Please review.

Project coverage is 74.9182%. Comparing base (a21c95b) to head (44ead1b).
Report is 5 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58512        +/-   ##
================================================
+ Coverage   73.5387%   74.9182%   +1.3794%     
================================================
  Files          1681       1726        +45     
  Lines        464263     473435      +9172     
================================================
+ Hits         341413     354689     +13276     
+ Misses       102025      96414      -5611     
- Partials      20825      22332      +1507     

Flag	Coverage Δ
integration	49.1839% <64.7058%> (?)
unit	72.2649% <73.5294%> (-0.0407%)	⬇️

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	61.6388% <ø> (+15.8642%)	⬆️