Use postgres_foreign_keys view for constraint validations

The following discussion from !1350 (merged) should be addressed:

• @stomlinson started a discussion:

  If we plan to do a lot more of these, we might benefit from the postgres_foreign_keys view defined in the rails project:

  https://gitlab.com/gitlab-org/gitlab/-/blob/master/db/structure.sql?ref_type=heads#L20731

  It has a lot of nice features. It can check if the constraint is validated, look at partitioning relationships between keys, and deal with text names rather than using ::regclass.