DOC: refactor main landing page to highlight archive backing

The modules that are supported by the archives should be highlighted, in fact the current sections organized by following the astroquery API or not should be refactored.
E.g. currently a user can get no insight into whether a module is fully backed with bugfixes, following the official server-side API, etc, or reversed engineered and maintained on a best-effort base. I think highlighting the ones that do have the official support is well deserved as well as super informative.

This is another part of a long overdue documentation refactoring (along with https://github.com/astropy/astroquery/issues/2416)

Start by locating the main landing page and reviewing how its modules are currently grouped by Astroquery API support. Read the related documentation refactoring issue #2416, then define the archive-support categories and update the landing page so official backing, API coverage, and best-effort reverse engineering are distinguishable.

Written by the indexing model from the issue text.