Set up alpha/secondary/experiments server

As detailed in https://anagora.org/mastodon-upgrade and discussed in the TWG chat room (https://anagora.org/go/twg/chat is the short link I use) and Loomio, the TWG would like to have a secondary server for experiments and training (e.g. to let new TWG members do drills like backup restores).

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information