* Add ability to change MQTT topic and or gateway name by MQTT command.
This adds new commands to allow changing the MQTT topic and or gateway name from a command.
The new topic/name will be saved in flash memory and used on subsequent reboots.
Either/both parameters can be sent or combined with other commands.
Example use:
```
mosquitto_pub -t "home/OpenMQTTGateway/commands/MQTTtoSYS/config" -m
'{
"mqtt_topic": "topic/",
"gateway_name: "name"
}'
```
* Update example with /
Co-authored-by: Florian <1technophile@users.noreply.github.com>
