fix(blooms): Skip multi-tenant TSDBs during bloom planning

[salvacorts]

What this PR does / why we need it:
Tables that have not been fully compacted yet will have multi-tenant TSDBs for which the tenant is "" (coming tsdbStore.UsersForPeriod and indexStorageClient.ListFiles)

In this PR we update the planner to skip these multi-tenant TSDBs.

I though about fixing this at the indexStorageClient.ListFiles level but I think it's relatively risky given it's is used in the compactor.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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