Move common host features to features-nixos folder

features-nixos/optional/avahi.nix

@@ -0,0 +1,12 @@
+{
+  # MDNS on local network
+  services.avahi = {
+    enable = true;
+    nssmdns4 = true;
+    nssmdns6 = true;
+    publish.enable = true;
+    publish.addresses = true;
+    ipv4 = true;
+    ipv6 = true;
+  };
+}