Elevate product areas in documentation

Created by: christinaforney

Elevating product features in the left nav (and moving docs directories to match).

Looks like this:

If you look at commits, first you can see the renames, then the updates too all the links separated by product area. Tagging one person from each team to verify the links for their area.

There is now a "Getting started area" that is still the same document from "Usage" and includes the tour. I will be improving these docs content ASAP.

Note: search had to be renamed to code_search because of the overlap with the docs search functionality.