Update default certificate of Github (#1322)

So as to enable updates with a payload without the cert, and add a command example. Also so change the update message to notice level

docs/use/gateway.md

@@ -115,6 +115,16 @@ The `server_cert` parameter is optional. If the update server has changed or cer
 :::
 
 ### Example firmware update message:
+Without certificate, in this case we will use the root certificate defined in User_config.h
+```
+mosquitto_pub -t "home/OpenMQTTGateway_ESP32_BLE/commands/firmware_update" -m '{
+  "version": "test",
+  "password": "OTAPASSWORD",
+  "url": "https://github.com/1technophile/OpenMQTTGateway/releases/download/v0.9.12/esp32dev-ble-firmware.bin"
+}'
+```
+
+With certificate:
 ```
 mosquitto_pub -t "home/OpenMQTTGateway_ESP32_BLE/commands/firmware_update" -m '{
   "version": "test",
@@ -150,7 +160,6 @@ A bash script is available [here](ota_command_cert.zip) to simplify the use of t
 The pre-built binaries for **rfbridge** and **avatto-bakeey-ir** have the above WiFi and MQTT broker credentials and the Firmware update via MQTT options disabled. This is due to the restricted available flash, so as to still be able to use OTA firmware updates for these boards.
 :::
 
-
 # State LED usage
 
 The gateway can support up to 3 LED to display its operating state: