coordinator: clean stale owner checkpoint metrics (#5491)

[ti-chi-bot]

This is an automated cherry-pick of #5491

What problem does this PR solve?

Issue Number: close #5490

Finished or removed changefeeds can leave stale ticdc_owner_checkpoint_ts_lag series visible. Finished changefeeds remain in the coordinator changefeed DB as stopped metadata, but the owner metrics loop only skipped StateStopped and kept setting checkpoint lag for StateFinished. Old owner instances could also keep checkpoint labels after ownership stops.

What is changed and how it works?

This PR deletes owner checkpoint timestamp and lag labels together for stopped, finished, or removed changefeeds instead of recreating them during the metrics loop. It also resets owner checkpoint labels when the coordinator metrics loop exits, so an instance that loses ownership stops exposing stale checkpoint series. The stop/remove path now deletes both checkpoint_ts and checkpoint_ts_lag.

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

No. This only changes cleanup behavior for owner metrics labels.

Do you need to update user documentation, design documentation or monitoring documentation?

No.

Release note

Fix stale owner checkpoint lag metrics for finished or removed changefeeds.

Summary by CodeRabbit

• Bug Fixes

  • Fixed metric cleanup for stopped changefeeds to prevent stale metrics from persisting in monitoring systems.
  • Improved periodic reset of changefeed metrics to ensure monitoring accuracy.

• Tests

  • Added tests to verify metrics are properly cleaned up when changefeeds reach terminal states.

[ti-chi-bot]

@asddongmen 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]

@ti-chi-bot: ## If you want to know how to resolve it, please read the guide in TiDB Dev Guide.

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ti-chi-bot]

Cherry-pick conflicts appear resolved; removing the do-not-merge/hold label.

[asddongmen]

/test all

[asddongmen]

/retest