coordinator: force update gc safepoint when creating changefeed

[3AceShowHand]

What problem does this PR solve?

Issue Number: close #xxx

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[gemini-code-assist]

Summary of Changes

Hello @3AceShowHand, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a potential race condition or data loss scenario by ensuring that the garbage collection (GC) safepoint is forcefully and proactively updated when a new changefeed is created. By adjusting the order of operations and introducing a force flag to GC management functions, the system can prevent necessary data from being prematurely garbage collected, thereby enhancing the reliability of changefeed creation.

Highlights

• GC Safepoint Update Order: The logic for updating the GC safepoint during changefeed creation has been reordered. The updateGCSafepointByChangefeed call now occurs before the CreateChangefeed operation in the controller, ensuring the safepoint is set proactively.
• Forced GC Safepoint Updates: A new force boolean parameter has been introduced to updateGlobalGcSafepoint and updateKeyspaceGcBarrier functions. When creating a changefeed, these functions are now called with force=true, ensuring the GC safepoint is updated immediately.
• Improved Error Handling for Keyspace Barriers: The updateAllKeyspaceGcBarriers function now logs warnings for individual keyspace GC barrier update failures but continues processing other barriers, returning an aggregated error at the end.
• Minor Refactoring: The initialization of gcTicker in the run method was reordered to appear after a failpoint.Inject block, which is a minor structural change.

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Code Review

This pull request refactors the GC safepoint update mechanism, primarily by introducing a "force" parameter to control whether the GC safepoint update should be forced or follow the regular update interval. The CreateChangefeed function now forces a GC safepoint update before creating a new changefeed, which aligns with the PR's objective. Additionally, the error logging in CreateChangefeed has been improved. However, there's a potential issue with error handling in updateAllKeyspaceGcBarriers that could mask multiple failures.

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