docs: Document JournalNodes are not exposed (#535)

* docs: Document JournalNodes are not exposed

* Update docs/modules/hdfs/pages/usage-guide/listenerclass.adoc

Co-authored-by: Felix Hennig <fhennig@users.noreply.github.com>

---------

Co-authored-by: Felix Hennig <fhennig@users.noreply.github.com>

Author: sbernauer

docs/modules/hdfs/pages/usage-guide/listenerclass.adoc

@@ -2,6 +2,8 @@
 
 The operator deploys a xref:listener-operator:listener.adoc[Listener] for each DataNode and NameNode pod. They both default to only being accessible from within the Kubernetes cluster, but this can be changed by setting `.spec.{data,name}Nodes.config.listenerClass`.
 
+Note that JournalNodes are not accessible from outside the Kubernetes cluster.
+
 The cluster can be configured to be accessible from outside of Kubernetes like this:
 
 [source,yaml]