Federate Global search with .com marketing search and document search.

For authenticated users, the Navbar search is the most president search bar. Sometimes Authenticated users will need to leave the GitLab experience to search for documents and information on marketing pages.

While using GitLab is the primary case it might be possible to federate the experience by including tabs and to return results from the other Search APIs.

These would be a lower priority so I would consider them being added under something like "More categories" I would not anticipate including these in the elastic search index at this time.

This is sort of done today with how we search epics but do not have them indexed.