[SYS] Add save option to discovery and ohdiscovery key and remove discovery for Arduino boards (#1696)

Enabling to keep discovery off if required

Remove Mqtt discovery for Arduino UNO and ATMEGA

docs/use/gateway.md

@@ -27,7 +27,8 @@ You can deactivate the MQTT auto discovery function, this function enables to au
 ### Activate
 `mosquitto_pub -t "home/OpenMQTTGateway/commands/MQTTtoSYS/config" -m '{"discovery":true}'`
 
-If you want the settings to be kept upon gateway restart, you can publish the command with the retain flag.
+If you want the settings to be kept upon gateway restart, you can save the state by adding `"save":true` (ESP32 only).
+`mosquitto_pub -t "home/OpenMQTTGateway/commands/MQTTtoSYS/config" -m '{"discovery":false, "save":true}'`
 
 ::: tip
 Auto discovery is enable by default on release binaries, on platformio (except for UNO). With Arduino IDE please read the [advanced configuration section](../upload/advanced-configuration#auto-discovery) of the documentation.
@@ -38,6 +39,9 @@ OpenHAB does not support the key `is_defined` in the json template, to remove it
 
 `mosquitto_pub -t "home/OpenMQTTGateway/commands/MQTTtoSYS/config" -m '{"ohdiscovery":true}'`
 
+If you want the settings to be kept upon gateway restart, you can save the state by adding `"save":true` (ESP32 only).
+`mosquitto_pub -t "home/OpenMQTTGateway/commands/MQTTtoSYS/config" -m '{"ohdiscovery":true, "save":true}'`
+
 ::: tip
 This command can also be used with other controllers that does not support the is_defined key.
 :::