On artist pages on the website, we only show release groups containing official releases by default. There's no mechanism to get the same list of "official" release groups via a browse request in the web service – we only support status filtering on /ws/2/release. I propose we support status=official filtering on /ws/2/release-group, too. This should be efficient to implement, since it's stored in the artist_release_group table; I'd limit it to official for now unless people have a solid use case for other types.

This idea came about from SEARCH-667 where user discocat is trying to get the same results via the search server, but can't due to the paged responses being inconsistent.

The final implementation to get the same results as in the "official" view on the MB website is "release-group-status=website-default" (with "all" giving all release groups, same as not actually passing the option). We might add other options in the future ("unofficial" only is trivial, specific statuses a bit less so but still doable) - request as needed.