Call out crdb_internal.interleaved in interleaved tables deprecation docs

[vy-ton]

In cockroachdb/cockroach#58867, we added a crdb_internal table to help users detect their interleaved table and index usage. We should highlight this table in the before the step to convert interleaved tables.

[vy-ton]

@ericharmeling In the linked PR, I don't see a callout for crdb_internal.interleaved. Users should query that table to see if they have interleaved tables/indexes

[ericharmeling]

I don't see a callout for crdb_internal.interleaved.

I don't think cockroachdb/cockroach#61629 was backported to 21.1 or 20.2. So I didn't refer to crdb_internal.interleaved because that table only exists in 21.2, and, IIUC, users can't upgrade to 21.2 if they have interleaved tables.

[vy-ton]

Thanks for info, I'm following up on the backport