ttl: implement TTL scheduled job validation & fixup

[cockroach-teamcity]

Exalate commented:

cockroachdb/cockroach#77741 --- Release note (sql change): Adds a crdb_internal.repair_ttl_table_scheduled_job builtin, which repairs the given TTL table's scheduled job by supplanting it with a valid schedule.

Jira Issue: DOC-2982