(Azure CXP) resolves MicrosoftDocs/azure-docs#55135

The az aro create is missing the trigger --apiserver-visibility Private which makes the apiserver private.
Updated the code with the argument.

Author: VikasPullagura-MSFT

articles/openshift/create-private-cluster.md

@@ -190,7 +190,8 @@ az aro create \
   --name $CLUSTER \
   --vnet aro-vnet \
   --master-subnet master-subnet \
-  --worker-subnet worker-subnet
+  --worker-subnet worker-subnet \
+  --apiserver-visibility Private
   # --domain foo.example.com # [OPTIONAL] custom domain
   # --pull-secret @pull-secret.txt # [OPTIONAL]
 ```