Complete <xs:documentation> for all configuration elements/attributes in Infinispan subsystem's XSD

Infinispan subsystem's XSD still contains a lot of elements/attributes which do NOT have their description: https://github.com/jbossas/jboss-as/blob/master/build/src/main/resources/docs/schema/jboss-as-infinispan_1_1.xsd

It would be very useful for users to know what each element is supposed to do.

This document can help out: https://docspace.corp.redhat.com/docs/DOC-69249