mcs: add affinity redirect and scheduling watcher (#10042)

[ti-chi-bot]

This is an automated cherry-pick of #10042

What problem does this PR solve?

Issue Number: Ref #9764

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

Summary by CodeRabbit

• New Features

  • Added affinity groups API endpoints and a background watcher to keep affinity state synced.
  • Introduced middleware to forward affinity-related requests to the scheduling service.

• Improvements

  • Better handling for label rules that arrive before their groups (buffering and reconciliation).
  • Centralized and expanded redirect matching logic and rule representation.

• Tests

  • Added extensive tests for watcher/manager lifecycle, concurrency, and redirect matching.

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick:

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[ti-chi-bot]

@lhy1024 This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ti-chi-bot]

@ti-chi-bot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-build-release-8.5	2b5dac6	link	true	/test pull-build-release-8.5

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