Make apex host specific to each machine

Allows direct contact via the VPN when accessing from fox, but use
Internet when using the rest of the machines.

Reviewed-by: Aleix Roca Nonell <aleix.rocanonell@bsc.es>

m/fox/wireguard.nix

@@ -32,4 +32,8 @@
       ];
     };
   };
+
+  networking.hosts = {
+    "10.100.0.30" = [ "apex" ];
+  };
 }