dunst: UWSM compatibility (#7472)

Added Install field for systemd service, which is needed for autostart to work properly under compositors launched under UWSM

modules/services/dunst.nix

@@ -218,6 +218,9 @@ in
                 ]
             );
             Environment = lib.optionalString (cfg.waylandDisplay != "") "WAYLAND_DISPLAY=${cfg.waylandDisplay}";
+            Install = {
+              WantedBy = config.wayland.systemd.target;
+            };
           };
         };
       }