Fix some old naming in usage doc

Author: nightkr

docs/modules/listener-operator/examples/listenerclass-public-gke.yaml

@@ -2,6 +2,6 @@
 apiVersion: listeners.stackable.tech/v1alpha1
 kind: ListenerClass
 metadata:
-  name: public
+  name: external-stable
 spec:
   serviceType: LoadBalancer

docs/modules/listener-operator/examples/listenerclass-public-onprem.yaml

@@ -2,6 +2,6 @@
 apiVersion: listeners.stackable.tech/v1alpha1
 kind: ListenerClass
 metadata:
-  name: public
+  name: external-stable
 spec:
   serviceType: NodePort

docs/modules/listener-operator/pages/listenerclass.adoc

@@ -113,6 +113,7 @@ The Stackable Data Platform assumes the existence of a few predefined ListenerCl
 `external-unstable`:: Used for listeners that are accessible from outside the cluster, but which do not require a stable address. For example: individual Kafka brokers.
 `external-stable`:: Used for listeners that are accessible from outside the cluster, and do require a stable address. For example: Kafka bootstrap.
 
+[#presets]
 === Presets
 
 To help users get started, the Stackable Listener Operator ships different ListenerClass _presets_ for different environments.

docs/modules/listener-operator/pages/usage.adoc

@@ -25,3 +25,5 @@ Or like this for on-premise environments:
 ----
 include::example$listenerclass-public-onprem.yaml[]
 ----
+
+These are normally installed by the appropriate xref:listenerclass.adoc#presets[preset].