Include postgresql-libpq

[phadej]

It's quite important lib:

• https://packdeps.haskellers.com/reverse/postgresql-libpq
• https://packdeps.haskellers.com/reverse/postgresql-simple

and only requires libpq-dev package do be installed on Debian based systems.

EDIT: hpqtypes also needs just libpq-dev

[Bodigrim]

I'd like to keep impact assessment accessible for Windows users. Maybe we can enable it under if !os(windows) section?..

[phadej]

There are a lot of packages which is harder to get working on windows. brotli needs a lib, magic needs a lib, proto-lens-protobuf-types needs protoc in scope. (EDIT: postgresql-libpq often just compiles when postgresql is installed, for which installers are available - that is how i test it locally). So the current state is far from easy to compile on windows. (incl #4).

[tbidne]

This is resolved by #18 fyi. postgresql-libpq is included except windows.