nixos/zigbee2mqtt: persist groups set via ui

        server = mkDefault "mqtt://localhost:1883";

      };

      serial.port = mkDefault "/dev/ttyACM0";

      # reference device configuration, that is kept in a separate file

      # reference device/group configuration, that is kept in a separate file

      # to prevent it being overwritten in the units ExecStartPre script

      devices = mkDefault "devices.yaml";

      groups = mkDefault "groups.yaml";

    };

    systemd.services.zigbee2mqtt = {