server: store the updated labels into etcd (#51451)

[ti-chi-bot]

This is an automated cherry-pick of #51451

What problem does this PR solve?

Issue Number: close #51427

Problem Summary:

What changed and how does it work?

Update the latest labels to etcd when label api is called.

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.

Ran the case described in the issue now got:

~ » curl 127.0.0.1:10080/info/all
{
...
   "labels": {},
...
}%
----------------------------------------------------------------------------------
~ » curl -X POST -d "{\"foo\": \"bar\"}" 127.0.0.1:10080/labels
{
 "foo": "bar"
}%
----------------------------------------------------------------------------------
~ » curl 127.0.0.1:10080/info/all
{
...
   "labels": {
    "foo": "bar"
   },
...
 }
}%
----------------------------------------------------------------------------------
~ » curl -X POST -d "{\"foo\": \"tidb\"}" 127.0.0.1:10080/labels                                                                                                                                                                                               you06@you06s-MBP
{
 "foo": "tidb"
}%
----------------------------------------------------------------------------------
~ » curl 127.0.0.1:10080/info/all
{
...
   "labels": {
    "foo": "tidb"
   },
...
}%

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

[you06]

/retest

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.1@1dc6edf). Click here to learn what that means.
The diff coverage is 54.5454%.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.1     #51564   +/-   ##
================================================
  Coverage               ?   73.4423%           
================================================
  Files                  ?       1212           
  Lines                  ?     379537           
  Branches               ?          0           
================================================
  Hits                   ?     278741           
  Misses                 ?      82993           
  Partials               ?      17803           

[you06]

/merge

[ti-chi-bot]

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[you06]

/approve

[you06]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, lcwangchao, you06, zimulala

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Needs approval from an approver in each of these files:

• OWNERS [hawkingrei,lcwangchao,you06,zimulala]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-07 07:20:00.796206435 +0000 UTC m=+324427.818452823: ☑️ agreed by hawkingrei.
• 2024-03-07 07:43:55.100752151 +0000 UTC m=+325862.122998540: ☑️ agreed by zimulala.