playground: make sure to signal tiproxy to stop

[dveeden]

What problem does this PR solve?

Closes #2317

What is changed and how it works?

Check List

Tests

• Manual test (add detailed scripts or steps below)

Related changes

• Need to cherry-pick to the release branch

Release notes:

TiUP Playground was updated to signal TiProxy to stop gracefully when stopping the playground.

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (bff409d) 55.52% compared to head (e638865) 55.51%.

❗ Current head e638865 differs from pull request most recent head 76d8e8f. Consider uploading reports for the commit 76d8e8f to get more accurate results

Files	Patch %	Lines
components/playground/playground.go	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2318      +/-   ##
==========================================
- Coverage   55.52%   55.51%   -0.01%     
==========================================
  Files         325      325              
  Lines       34725    34729       +4     
==========================================
- Hits        19280    19278       -2     
- Misses      13143    13147       +4     
- Partials     2302     2304       +2     

Flag	Coverage Δ
playground	15.25% <0.00%> (-<0.01%)	⬇️
tiup	33.48% <ø> (ø)
unittest	22.38% <0.00%> (+0.01%)	⬆️

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[kaaaaaaang]

/lgtm

[kaaaaaaang]

/approve

[ti-chi-bot]

@dveeden: Your PR was out of date, I have automatically updated it for you.

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[kaaaaaaang]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-15 05:45:08.721072042 +0000 UTC m=+4227906.308182188: ☑️ agreed by kaaaaaaang.
• 2023-11-15 05:45:29.060759743 +0000 UTC m=+4227926.647869884: ✖️🔁 reset by ti-chi-bot[bot].
• 2023-11-15 07:26:17.995436736 +0000 UTC m=+4233975.582546882: ☑️ agreed by kaaaaaaang.

[kaaaaaaang]

/approve

[ti-chi-bot]

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This pull-request has been approved by: kaaaaaaang

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