feat(influxdb3_system_tables): expose system.tables for all databases

[vrongmeal]

Closes #27205

Make the system.tables system table available for all databases, not just the internal database. When queried from a non-internal database, the results are scoped to only the tables in that database.

• I've read the contributing section of the project README.
• Signed CLA (if not already signed).

[philjb]

Thanks for your submission: @hiltontj is out for a little bit and will get back to you after returning.

[hiltontj]

Hey @vrongmeal thanks for submitting a PR. The implementation looks clean and straight-forward.

At minimum, some tests are required:

• A test querying system.tables from a non-internal database and verifying results are scoped to that database only
• A test querying system.tables from _internal and verifying it still returns all databases (the None path)
• An edge case test for the error path when the database doesn't exist in the catalog (the ok_or_else on line 57-59 of the PR's tables.rs)

I think the place to write those tests would be influxdb3/tests/server/system_tables.rs.

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Someone on our team will need to vet this in Enterprise to verify that there are no authz-related issues with the implementation.

[vrongmeal]

Hey! Thanks for the review. Updated the PR addressing the comments.