This supersedes #1996 by reusing existing scaffolding we already have for many other objects.

As an aside this should have the added benefit of further decoupling the CLI because we actually use _repr_attr in the API itself which was not yet the case with _short_print_attr and it was a bit out of place in base.py IMO. Now, the CLi simply reuses it.

Note: @Psycojoker this replaces name_with_namespace in your PR with path because we already had it and it'd otherwise be a breaking change on the CLI. Let me know if you want to override that, otherwise we'll use with_namespace in the next major release which I hope we can have soon with some other features. In any case I think the least confusing option would be path_with_namespace because people can name the group and project anything they like, so my-evil-group/my-evil-project can be named to display as GitLab.org / GitLab if using names.