feat(stream): namespace metrics for unaligned join logstore

[kwannoel]

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What's changed and what's your intention?'

Separate metrics from connector metrics

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

• My PR needs documentation updates.

Release note

[kwannoel]

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(frontend): add AddLogStore rule #20386
• feat(frontend): support logstore plan node #20376
• feat(stream): namespace metrics for unaligned join logstore #20375 👈 (View in Graphite)
• feat(stream): add synced logstore #20204 : 1 other dependent PR (#20262 )
• main

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