Changing Port used for MQTT in ESP8266

[Jakob-B]

It appears that the MQTT port (1883) used by ESP8266 is hardcoded. However, in some cases it would be useful to change the port used for MQTT, ideally also using the node.conf or system.conf file. (I know that 1883 is a standardized port for MQTT, but would be a nice feature that could come in handy i.e. for debugging)