server: add initial status server to provide debug functionalities before starting server

[YangKeao]

What problem does this PR solve?

Issue Number: close #59087

Problem Summary:

The /debug/pprof/xxx endpoints in status server and the signal handler of SIGUSR1 are very helpful for the developers to debug running tidb-server. However, they are only available after starting the server. If the TiDB server is somehow blocked before starting successfully (like loading InfoSchema for a very long time), it'll be hard for us to investigate the issue.

What changed and how does it work?

1. Set the signal handler before most of the bootstrap logic.
2. Start an initial status server which only handles several /debug/pprof/xxx interface and /metrics interface.
3. Stop the initial status server before starting the real fully functional status 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.

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

None

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 22 lines in your changes missing coverage. Please review.

Project coverage is 73.4910%. Comparing base (837b1f5) to head (d973c99).
Report is 9 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #59122        +/-   ##
================================================
+ Coverage   73.0925%   73.4910%   +0.3985%     
================================================
  Files          1684       1684                
  Lines        466350     467408      +1058     
================================================
+ Hits         340867     343503      +2636     
+ Misses       104548     102952      -1596     
- Partials      20935      20953        +18     

Flag	Coverage Δ
integration	42.7968% <66.6666%> (?)

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	45.3290% <ø> (+0.0086%)	⬆️

[YangKeao]

The only concern is that the requests to /debug/pprof/profile will block the Shutdown for a long time (so I gave it a 5s timeout).

It's also fine to Close directly IMO, but I'm not sure which one is better.

[ti-chi-bot]

@YangKeao: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/build	d973c99	link	true	/test build
idc-jenkins-ci-tidb/unit-test	d973c99	link	true	/test unit-test

Full PR test history. Your PR dashboard.

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