feat: Add Waypipe for Wayland forwarding

hosts/nixos-testbed/configuration.nix

@@ -75,6 +75,10 @@
     git
     git-annex
     sydnix-cli.packages.x86_64-linux.default
+
+    # Waypipe provides the equivalent of X11 forwarding for Wayland.  This is a
+    # VM, so it's very handy.
+    waypipe
   ];
 
   services.openssh = {