[Search] Irrational search scoping
Our global search will never be fast on big instances while we have this in our code (neither regular search nor ES search):
https://gitlab.com/gitlab-org/gitlab-ee/blob/v8.5.0-ee/app/services/search/global_service.rb#L13
https://gitlab.com/gitlab-org/gitlab-ee/blob/v8.5.0-ee/app/services/search/snippet_service.rb#L10
I created this issue in EE because it should be fixed simultaneously for ES and DB search (probably).