[Discovery] Re-add the discovery switch

revert #1365, indeed the switch may be usefull to avoid non desirable discovery of RTL_433 or BT devices  #1487

main/ZmqttDiscovery.ino

@@ -516,6 +516,15 @@ void pubMqttDiscovery() {
                   "", "", "", "", false, // device name, device manufacturer, device model, device ID, retain
                   stateClassNone //State Class
   );
+  createDiscovery("switch", //set Type
+                  "", "SYS: Auto discovery", (char*)getUniqueId("discovery", "").c_str(), //set state_topic,name,uniqueId
+                  will_Topic, "", "", //set availability_topic,device_class,value_template,
+                  "{\"discovery\":true}", "{\"discovery\":false}", "", //set,payload_on,payload_off,unit_of_meas,
+                  0, //set  off_delay
+                  Gateway_AnnouncementMsg, will_Message, true, subjectMQTTtoSYSset, //set,payload_avalaible,payload_not avalaible   ,is a gateway entity, command topic
+                  "", "", "", "", true, // device name, device manufacturer, device model, device MAC, retain,
+                  stateClassNone //State Class
+  );
 #    endif
 #    ifdef ZboardM5STACK
   createDiscovery("sensor", //set Type