mumble: init clan-module

This adds the `mumble` clan-module.

This allows for voice chatting in a true peer-to-peer network.
Every machine that has the module enabled is a potential host and
client - every participant has the same role.

It doesn't matter who in the network is online - as long as one of the
machines is up, one server is up and people can start their voice chat.

clanModules/flake-module.nix

@@ -11,6 +11,7 @@
     matrix-synapse = ./matrix-synapse;
     moonlight = ./moonlight;
     packages = ./packages;
+    mumble = ./mumble;
     postgresql = ./postgresql;
     root-password = ./root-password;
     sshd = ./sshd;