Is your feature request related to a problem? Please describe.
With DB-level changefeeds, and especially withtheir need to apply table filters, the delegate query for SHOW CHANGEFEED JOBS has many CTEs and has become hard to reason about.

Describe the solution you'd like
SHOW CHANGEFEED JOBS should be implemented as an opaque statement.

Describe alternatives you've considered
I implemented the query as a delegate https://github.com/cockroachdb/cockroach/pull/156873, but it's difficult for reviewers to follow. I've attempted a few different ways, but the intermediate CTEs remain difficult to parse.

Jira issue: CRDB-56942

Epic CRDB-55919