nix: add portals.conf file

nix/nixos-modules.nix

@@ -26,6 +26,25 @@ in {
     xdg.portal = {
       enable = lib.mkDefault true;
 
+      config = {
+        mango = {
+          default = [
+            "gtk"
+          ];
+          # except those
+          "org.freedesktop.impl.portal.Secret" = ["gnome-keyring"];
+          "org.freedesktop.impl.portal.ScreenCast" = ["wlr"];
+          "org.freedesktop.impl.portal.ScreenShot" = ["wlr"];
+
+          # wlr does not have this interface
+          "org.freedesktop.impl.portal.Inhibit" = [];
+        };
+      };
+      extraPortals = with pkgs; [
+        xdg-desktop-portal-wlr
+        xdg-desktop-portal-gtk
+      ];
+
       wlr.enable = lib.mkDefault true;
 
       configPackages = [cfg.package];