docs: Metrics are available on different port on kubernetes (#288)

Author: franck-dailymotion

docs/managing-dragonfly/monitoring.md

@@ -7,3 +7,14 @@ sidebar_position: 5
 By default, Dragonfly allows HTTP access via its main TCP port (i.e, `6379`) and it exposes Prometheus compatible metrics on `:6379/metrics`.
 
 Check out this complete example of setting up a [Grafana Monitoring Stack with Dragonfly](https://github.com/dragonflydb/dragonfly/tree/main/tools/local/monitoring).
+
+** :warning: **
+
+If you're using kubernetes, Metrics are also available on admin port `9999`. You may encounter this error with port `6379`:
+
+```
+* Request completely sent off
+* Received HTTP/0.9 when not allowed
+* Closing connection
+curl: (1) Received HTTP/0.9 when not allowed
+```