*: fix empty SQL in slow log for internal statement (#54274)

[ti-chi-bot]

This is an automated cherry-pick of #54274

What problem does this PR solve?

Issue Number: close #54190 , close #52743 , close #53264

What changed and how does it work?

The internal session does not init EnableRedactLog which cause redact.String always returns empty string.

Init it as an default value in this PR.

Check List

Tests

• [ ] Unit test
• [ ] Integration test
• [x] Manual test (add detailed scripts or steps below)

set @@tidb_slow_log_threshold=0;

And check the output slow logs. No empty strings again.

• [ ] 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.

fix empty SQL in slow log for internal statement

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.1@ef173c6). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #54309   +/-   ##
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  Coverage               ?   71.5714%           
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  Branches               ?          0           
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  Hits                   ?     304731           
  Misses                 ?     100634           
  Partials               ?      20407           

Flag	Coverage Δ
unit	71.5714% <60.0000%> (?)

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Components	Coverage Δ
dumpling	53.9957% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	40.9230% <0.0000%> (?)

[lcwangchao]

/retest

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-06-29 10:50:35.855254482 +0000 UTC m=+1062362.340743313: :ballot_box_with_check: agreed by lcwangchao.
• 2024-07-29 06:41:11.451292315 +0000 UTC m=+165187.731340385: :ballot_box_with_check: agreed by xhebox.

[lcwangchao]

/approve

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lcwangchao, xhebox, yudongusa

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Needs approval from an approver in each of these files:

• ~~OWNERS~~ [lcwangchao,xhebox]
• ~~pkg/sessionctx/variable/OWNERS~~ [yudongusa]

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[lcwangchao]

/retest