[EAP-7.4.Beta]Add mixed domain information for 7.3 / 7.4

Original JIRA note:
There is currently a section [1] in the Configuration Guide that discusses how to handle managed domains with different versions of EAP. For example, you can configure an EAP 7.1 host to manage EAP 7.0 hosts or EAP 6.4 hosts.

We need to determine whether a new section needs to be added for 7.2 EAP hosts to manage previous versions of EAP in a managed domain.

[1] https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.1/html-single/configuration_guide/#managing_multiple_jboss_eap_versions

^^ Update for 7.4.beta context.