filemanager: remove database requirement to compile code

[mmalenic]

We should consider removing the requirement on a postgres database to compile code. While this was initially a good feature in early development, I think it's not that useful anymore and tends to get in the way as most tools just don't expect code compilation to require database access. See #429 and #529.

This would involve turning any sqlx query! calls into function calls using query(), as these don't require database access. It would also mean removing the filemanager-build sea-orm entity generation step and instead adding the generated entities into the code base.

I think this change would be beneficial, as it would reduce the hassle of compiling the filemanager codebase and also probably improve compile times.