feat: support ibis.postgres.connect("postgresql://...") in addition to ibis.connect("postgresql://...")

[NickCrews]

Is your feature request related to a problem?

ibis.connect("postgresql://...") already works, but in my app I started with ibis.postgres.connect("postgresql://...") and this failed, so I started filing this issue before I looked at the code and discovered the workaround.

What is the motivation behind your request?

No response

Describe the solution you'd like

I think this is already implemented in other backends, so just emulate what they do? I could write a PR but I'm not sure how to write the tests. If this is simple for you then awesome, otherwise let me know and I can put in the time to write the PR.

What version of ibis are you running?

main

What backend(s) are you using, if any?

postgres

Code of Conduct

• I agree to follow this project's Code of Conduct

[cpcloud]

This doesn't work for any backend. It used to work, and it made the implementation of connect unnecessarily complicated.

If you want to use URLs to connect, then you go through ibis.connect, otherwise you use ibis.${backend}.connect.

I see that you didn't fill out the motivation part ... so what's the motivation here?