Include patch in the email notification about revisions

As discussed on #hackage, receiving a patch/pr/mr when a revision is made would help make the update flow back upstream.

Hackage can already send an email notification when a revision happens, so I think it makes sense to include a patch in the email. Plus, this method is forge-agnostic as opposed to integration with github/gitlab/codeberg/...

If the email address the patch is sent to is configurable separately from the main email address, we'd also get free integration with mailing lists (sourcehut etc)