`cookiebar.js` can only accept all cookie groups

[krmax44]

As far as I can tell, there is currently no way to specify which cookie groups to accept/decline with cookiebar.js. It's either accept or decline all. Maybe that's too complex for a generic cookiebar.js component, but it'd be nice if FetchClient could have some methods like acceptCookieGroups(groups: string[]).

[sergei-maertens]

@krmax44 yeah that seems like a sensible feature request! I do however want to first clean up the backend views for the accept/decline, because I'm not too charmed by the parameter encoding in the URL.