[Add forge now] include phabricator in forge types

Summary:

The coverage page mentions that Phabricator is a supported forge type, but the Add forge now page does not include phabricator amongst the supported forge types that end-users can submit for archiving.

Plan:

• Implement lister
• Implement loader
• docker: Run lister
• docker: Run loader
• Document lister
• Document loader
• Deploy on staging
• Call for public review
• Deploy on production