Support `gh:` and `gl:` prefixes for Copier

### Describe the proposed change(s).

As noted in #35577, it'd be useful for Renovate's [Copier manager support](https://docs.renovatebot.com/modules/manager/copier/) to support the `gh:` and `gl:` prefix, to automagically expand to the `github.com` and `gitlab.com` variants accordingly