deploy GitLab postgresql server from our existing infrastructure

we should consider deploying the PostgreSQL database server and Prometheus monitoring (done) from our existing puppet recipes instead of using the omnibus versions.

pgsql, in particular, is causing us troubles because our normal backup procedures do not work.

prometheus is also causing issues because we cannot reuse our export/realize resources in puppet (see https://gitlab.torproject.org/tpo/tpa/services/-/issues/34420, https://gitlab.torproject.org/tpo/tpa/services/-/issues/33921) fixed