system: Set flatpak as module

modules/system/apps/flatpak/default.nix

@@ -0,0 +1,17 @@
+{ config, lib, ... }:
+
+with lib;
+let
+  cfg = config.modules.system.apps.flatpak;
+in
+{
+  options.modules.system.apps.flatpak = {
+    enable = mkEnableOption ''
+      Enable flatpak
+    '';
+  };
+
+  config = mkIf cfg.enable {
+    services.flatpak.enable = true; # Important can't be enabled from home-manager
+  };
+}