MQTT Gateway Client - Last Will topic and feature

[cloolalang]

MQTT Gateway Client - Last Will topic and feature.

It would be really nice if our controllers can know if the gateway disconnects.

I think this can be implemented in MyGatewayTransportMQTTClient.cpp

bool reconnectMQTT(void)
{
GATEWAY_DEBUG(PSTR("GWT:RMQ:CONNECTING...\n"));
// Attempt to connect
if (_MQTT_client.connect(MY_MQTT_CLIENT_ID, MY_MQTT_USER, MY_MQTT_PASSWORD))