ISPN-4363 Add documentation for Cluster Listeners

* Added documentation about cluster listeners
* Added documentation about filters
* Added documentation about retry

https://issues.jboss.org/browse/ISPN-4363
1: For cluster listeners a KeyValueFilter is not required, this is only for the EntryRetriever.  I will update that since I was thinking of the latter when I wrote this.
2. The key will always be sent, however the Converter can change the resulting value to technically anything you want, it could even return null if you wanted do a more performant keySet for example.