chore: add version mangement and reorganize data in nammed docker volume

.gitignore

@@ -1 +1 @@
-auth.db
+/etc

docker-compose.yml

@@ -1,18 +1,22 @@
 services:
   ntfy:
-    image: binwiederhier/ntfy:latest
+    image: binwiederhier/ntfy:v2.16
     container_name: ntfy
     restart: always
     command:
       - serve
     volumes:
-      - /var/cache/ntfy:/var/cache/ntfy
-      - /etc/ntfy:/etc/ntfy
+      - ntfy_cache:/var/cache/ntfy
+      - ./etc:/etc/ntfy
     env_file:
       - ntfy.env
     networks:
       - reverse-proxy
 
+volumes:
+  ntfy_cache:
+    external: true
+
 networks:
   reverse-proxy:
     external: true