feat: delete Kafka consumer group when source backfill is finished

[xxchan]

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What's changed and what's your intention?

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Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
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• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

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Release note

Now Kafka consumer groups created by RisingWave Kafka source during backfill will be deleted when the backfill process is finished.

[xxchan]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat: delete Kafka consumer group when source backfill is finished #20077 👈 (View in Graphite)
• feat: delete Kafka consumer group on drop #20065
• refactor(meta): splits source_manager into smaller mods #20071
• main

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