Add mz_internal.mz_kafka_source_tables introspection table for kafka source tables

[rjobanp]

Motivation

Part of the work in #29373

This change is also detailed in the design doc: https://github.com/MaterializeInc/materialize/blob/main/doc/developer/design/20240625_source_versioning__table_from_sources.md#system-catalog--introspection-updates

Tips for reviewer

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[kay-kim]

lgtm from docs side mod couple of nits (feel free to ignore)