watchtower: track v1 and enable self-updates

watchtower/docker-compose.yaml

@@ -1,8 +1,10 @@
 services:
   watchtower:
-    image: nickfedor/watchtower:latest
+    image: nickfedor/watchtower:1
     container_name: watchtower
     restart: unless-stopped
+    labels:
+      - "com.centurylinklabs.watchtower.enable=true"
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock
       - ~/.docker/config.json:/config.json:ro