Add "server_cert" parameter to firmware_update command. (#1043)

When updating from the MQTT command from a SSL enabled server this adds an option to provide
the server SSL certificate with the command.

This is useful if connecting to different servers or if the configured certificate has expired
and requires updating to not lose the ability to update via OTA.

The certificate provided will be saved to flash memory for use on subsequent restarts.

docs/use/gateway.md

@@ -97,19 +97,44 @@ The gateway can be updated through an MQTT message by providing a JSON formatted
 To enable this functionality, `MQTT_HTTPS_FW_UPDATE` will need to be defined or the line that defines in in user_config.h will need to be uncommented.
 
 ::: tip
-If using an unsecure MQTT broker it is **highly recommended** to disable the password checking by setting the macro `MQTT_HTTPS_FW_UPDATE_USE_PASSWORD` to 0 (default is 1 (enabled)), otherwise a clear text password may be sent over the network.
+If using an unsecure MQTT broker it is **highly recommended** to disable the password checking by setting the macro `MQTT_HTTPS_FW_UPDATE_USE_PASSWORD` to 0 (default is 1 (enabled)), otherwise a clear text password may be sent over the network.  
+
+The `server_cert` parameter is optional. If the update server has changed or certificate updated or not set in `user_config.h` then you can provide the certifiate here.
 :::
 
 ### Example firmware update message:
 ```
-mosquitto_pub -t "home/<gateway_name>/commands/firmware_update" -m
-'{
+mosquitto_pub -t "home/<gateway_name>/commands/firmware_update" -m '{
   "version": "test",
   "password": "OTAPASSWORD",
-  "url": "https://github.com/1technophile/OpenMQTTGateway/releases/download/v0.9.6/esp32-m5stack-ble-firmware.bin"
-}'
+  "url": "https://github.com/1technophile/OpenMQTTGateway/releases/download/v0.9.7/esp32dev-ble-firmware.bin",
+  "server_cert": "-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----"}'
 ```
 
+A bash script is available [here](ota_command_cert.zip) to simplify the use of the `server_cert` parameter.  
+
 # State LED usage
 
 The gateway can support up to 3 LED to display its operating state: