Trigger firmware update via MQTT (ESP Only). (#953)

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.

platformio.ini

@@ -830,6 +830,7 @@ lib_deps =
 build_flags =
   ${com-esp.build_flags}
   '-DSECURE_CONNECTION'
+  '-DMQTT_HTTPS_FW_UPDATE'
   '-DGateway_Name="OpenMQTTGateway_TEST_TLS"'
 board_build.flash_mode = dout
 
@@ -842,6 +843,7 @@ lib_deps =
 build_flags =
   ${com-esp.build_flags}
   '-DSECURE_CONNECTION'
+  '-DMQTT_HTTPS_FW_UPDATE'
   '-DGateway_Name="OpenMQTTGateway_TEST_TLS"'
 board_build.flash_mode = dout