If enabled in user_config.h this will trigger the OMG to update it's firmware from the link
provided in the MQTT message.
Example message:
{\"version\":\"test\",\"password\":\"OMGPASSWORD\",\"url\":\"https://github.com/1technophile/OpenMQTTGateway/releases/download/v0.9.6/esp32dev-ble-cont-firmware.bin\"}
If the firmware version in the message is not the same as the current OMG version the device will self update using the link in the url of the message.
