Support for the user specified version of the init command

[ongchi]

In current version, user pass path to pg_config tool or download to use local installed or download and build from source from postgres latest release tarball.

This pr extends init option to support custom version:

cargo pgrx init --pg12 12.10

Passing latest as option will also download and install the latest version from source release, which is identical to download, while the download option still remains for backward compatibility.

Closes: #149

[eeeebbbbrrrr]

I haven’t looked at the PR yet but I’m not keen on this idea.

We’ve already had a PR for this and I didn’t find the argument very persuasive. EDIT: sorry I guess it was the issue linked above.

If pgrx is to support specific major versions then it needs a lot more consideration than just this.

I still think the correct way to handle this workflow is to install that version locally yourself and use cargo pgrx init with a different PGRX_HOME.

In day-to-day development of a pgrx extension there should be no differences between point releases of a major version. So the only reason to install a specific one would be to evaluate an extension against an older Postgres that probably had a bug. I don’t see this as under pgrx’ perview.

[ongchi]

Thank you for your feedback and I understand your decision. I'll close this PR.