Removal of stale content from landing page and dropdown menu

Moving deprecated workshops (e.g. JBoss Data Virt and Cloud Forms) from content/workshops to content/retired would permit auto build of website to only host and maintain cards for active workshop content.
Also cleanup of OpenShift Service Mesh and replacement with zOpenShift Service Mesh would reduce confusion.

[ajacocks]

Discussing this with @mwanderson . Thanks!

[mwanderson]

Is the desire to create another menu item named "retired" and move the elements there?

[ajacocks]

Yes, that would be fine.