Provide ability to add a set of users for Business/Decision Central and Kie Server

Today we have a limited option to add users to PAM and DM images during the container creation.
The available environment variables responsible to create users are available here: https://github.com/jboss-container-images/jboss-kie-modules/blob/master/jboss-kie-wildfly-common/added/launch/jboss-kie-wildfly-security.sh#L10

And there is no way to provide, for example, multiple users for the authoring, process management/execution and/or users for access kieserver instances.

One idea would be provide a way to to configure it using environment variables in a similar way we do today for configuring multiple maven repositories.