publish method

Implementation

@override
Future<bool> publish(String topic, String msg) async {
  // connected?
  if (!connected) return false;

  final builder = MqttClientPayloadBuilder();
  builder.addString(msg);
  if (builder.payload != null) {
    client.publishMessage(topic, MqttQos.atMostOnce, builder.payload!);
  }

  return true;
}