ntfy: persist message cache for 1 week

ntfy.yaml

@@ -9,6 +9,8 @@ data:
     behind-proxy: true
     auth-file: /config/user.db
     auth-default-access: deny-all
+    cache-file: /config/cache.db
+    cache-duration: 168h
 ---
 apiVersion: apps/v1
 kind: Deployment