Include contrib/ in pgx init builds

[ewencp]

Specifically, this will make contrib extensions available so testing when they are needed can be done through the normal workflow.

[ewencp]

This could be hidden behind a flag to cargo pgx init, but I don't see much value in that since most extensions would need to be able to operate with others also available (and even loaded).

[eeeebbbbrrrr]

I'm gonna let CI chew on this just to make sure it all still works, but I don't really see a problem with this.

The question of "how do I install contrib package X?" has come up a few times over the years, so yeah, I think this just makes sense.

Would you mind updating the cargo-pgx/README.md to indicate that this is now what cargo pgx init does? If you'll do that, and CI passes, we'll get this merged and in the next point release.

[ewencp]

Sounds good, note added. Thanks!

[eeeebbbbrrrr]

I've installed quite a few of the contrib packages over the years, but I can't say I've installed every-single-one. I had a though of "are there extra system dependencies this will need?", but CI passed on both linux and mac so I think that was just my anxiety acting up for no good reason.

Merging. Thanks for the PR and welcome to the contributor club!