Make available our censorship snapshot over a domain-fronted URL

Over at tpo/community/outreach#28531, we're working on a censorship snapshot that summarises where and how Tor is blocked. The idea is that Tor Browser will use this snapshot to help the user figure out what circumvention method works. The question is: how does Tor Browser get this snapshot? It's not a good idea to hard-code it into Tor Browser because it will take a long time to update it. It's probably better for Tor Browser to fetch the snapshot each time it starts.

To guarantee that Tor Browser can always get the snapshot, even in the face of censorship, we should serve it over a domain-fronted endpoint, like we do for moat. There are several ways in which we could serve the snapshot:

• Polyanthum, the host that runs BridgeDB and rdsys, runs an Apache reverse proxy. We could serve the snapshot directly over Apache, which is probably the simplest solution.
• We could also teach rdsys how to serve the snapshot. Technically, the snapshot is a resource and rdsys is our resource distribution system.

Whatever solution we go with, we should make sure that we can easily and quickly update the snapshot if we learn of a new censorship event.