add serial number

devices/dimmer_serial_no.yaml

@@ -0,0 +1,8 @@
+- platform: template
+  name: 'Serial No.'
+  lambda: |-
+    std::string mac = get_mac_address();
+    return "dim" + mac.erase(0, mac.length()/2);
+  icon: mdi:expansion-card-variant
+  entity_category: diagnostic
+  update_interval: 10m