Adding unique device names to HA dicovery (#1270)

* Adding unique device names to HA dicovery

Multiple devices of the same model got the same name in Home Assistant,
making the device list less informative when there are many of e.g. the
same sensor.
To over come this changed the function publishing discovery messages to
add the second half of the device mac address to the device name so it
becomes unique.

Issue: #1269

main/ZmqttDiscovery.ino

@@ -333,7 +333,8 @@ void createDiscovery(const char* sensor_type,
     }
 
     if (device_name[0]) {
-      device["name"] = device_name;
+      // generate unique device name by adding the second half of the device_mac
+      device["name"] = device_name + String("-") + String(device_mac + 6);
     }
 
     device["via_device"] = String(gateway_name); //device name of the board