Allow use of PG environment variables along with .pgpass files

[will]

Thanks @wishdev! Could you though make one PR for adding the env vars and another for the pgpass? The reason being I think testing the env vars might be a little too much set up for CI, but the pgpass there could be some tests for.

Maybe if the pgpass was split up a bit so the parsing could at least be tested, it'd help make sure it doesn't silently break in the future

[wishdev]

@will I just pushed tests for all pieces - I did not break it up because I think testing everything covered your concerns here (if I read your comment correctly). I'm more than happy to break it up if that is still necessary

[will]

Thanks!