Search - Boost the current tenant

This is a simple addition that boosts search results from the current tenant. I suppose we'll have to play with the boost factor. This impacts searches when sharing resources with users and the general search.
I *think* function_score allows for that kind of thing. Whether it's performant is another question. I'm not convinced yet that we actually need boosting based on following, content, group memberships, .. And if we do, we might want to look at building proper user graphs.