Use `lib/pq`'s new `Config` struct

[louisroyer]

• https://pkg.go.dev/github.com/lib/pq#Config
• https://pkg.go.dev/github.com/lib/pq#example-NewConfig

This will also brings compatibility with standard $PG-prefixed env variables (but note that $PGFILE will not work in docker compose if passed as file via secret, because it is not possible to set the permission mode to o0600)