Add PostgresSequence view

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/139117



Merged-by: Matt Kasa <mkasa@gitlab.com>
Approved-by: Marius Bobin <mbobin@gitlab.com>
Approved-by: Matt Kasa <mkasa@gitlab.com>
Reviewed-by: Matt Kasa <mkasa@gitlab.com>
Co-authored-by: Maxime Orefice <morefice@gitlab.com>