refactor(meta): splits source_manager into smaller mods

[xxchan]

Signed-off-by: xxchan [email protected]

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What's changed and what's your intention?

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.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

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Release note

[xxchan]

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

approve as no logic change