[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

main/ZgatewayRF2.ino

@@ -131,7 +131,7 @@ void RF2toMQTT() {
     RF2data["address"] = (unsigned long)rf2rd.address;
     RF2data["switchType"] = (int)rf2rd.switchType;
 #  ifdef ZmqttDiscovery //component creation for HA
-    if (disc)
+    if (SYSConfig.discovery)
       RF2toMQTTdiscovery(RF2data);
 #  endif