sessionctx: refactor sessionctx pkg's warning and note generation

[AilinKid]

What problem does this PR solve?

Issue Number: close #49291

Problem Summary:

What changed and how does it work?

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.

sessionctx: refactor sessionctx pkg's warning and note generation

[tiprow]

Hi @AilinKid. Thanks for your PR.

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[codecov]

Codecov Report

Merging #49760 (12629a9) into master (660b1f3) will increase coverage by 0.4035%.
Report is 11 commits behind head on master.
The diff coverage is 51.3513%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #49760        +/-   ##
================================================
+ Coverage   70.9584%   71.3619%   +0.4035%     
================================================
  Files          1368       1428        +60     
  Lines        397089     416589     +19500     
================================================
+ Hits         281768     297286     +15518     
- Misses        95623     100482      +4859     
+ Partials      19698      18821       -877     

Flag	Coverage Δ
integration	43.8645% <51.3513%> (?)
unit	70.9569% <ø> (-0.0015%)	⬇️

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

Components	Coverage Δ
dumpling	53.9663% <ø> (ø)
parser	∅ <ø> (∅)
br	47.1999% <ø> (-5.7042%)	⬇️

[AilinKid]

/ok-to-test

[easonn7]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: easonn7, hawkingrei, qw4990

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Needs approval from an approver in each of these files:

• OWNERS [hawkingrei,qw4990]
• pkg/sessionctx/variable/OWNERS [easonn7]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-12-25 08:18:27.470414791 +0000 UTC m=+1467398.507641703: ☑️ agreed by hawkingrei.
• 2023-12-25 09:48:09.531047971 +0000 UTC m=+1472780.568274898: ☑️ agreed by qw4990.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #49766.