server: add a http interface to change labels

[glorv]

What problem does this PR solve?

Issue Number: ref #35926

Problem Summary:

What is changed and how it works?

This PR add a new interface under the status port to update tidb's labels config. tidb-operator depends on this interface to set some labels (e.g. zone) to the tidb server after the server is started. This is the same way as tidb-operator set tikv's labels to PD.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

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.

Support dynamically set server labels via http API

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• wjhuang2016
• xhebox

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/b4b78bca1ffcdc5a48b934828edc3363c5032ded

[xhebox]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 2bbe07c

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! [1] CI still failing after this pr merged.
These failed integration tests don't seem to be introduced by the current PR.

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/integration-common-test	🔴 failed 1, success 16, total 17	19 min	Existing failure
idc-jenkins-ci/integration-cdc-test	🟢 all 36 tests passed	26 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 11 tests passed	15 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	6 min 17 sec	Existing passed
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	5 min 47 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	5 min 39 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	5 min 18 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 50 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	3 min 18 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed

[kolbe]

@glorv why doesn't this PR include release notes?

[glorv]

@glorv why doesn't this PR include release notes?

Sorry. I originally thought this is a tiny change that needn't be included in the release note.