flake: rework modules folder structure

modules/nixos/services/printing.nix

@@ -0,0 +1,19 @@
+{ config, lib, ... }:
+{
+  options.settings.services.printing = {
+    enable = lib.mkEnableOption "enable printing";
+  };
+
+  config = lib.mkIf config.settings.services.printing.enable {
+    services = {
+      printing = {
+        enable = true;
+      };
+      avahi = {
+        enable = true;
+        nssmdns4 = true;
+        openFirewall = true;
+      };
+    };
+  };
+}