Add support for creating additional users and roles to the default security module based on property files

At the moment the base image only creates the admin user during initialization. There many use cases that requires adding additional users and roles to the default EAP security module based on property files. Especially for simple setups that do not require external Auth providers (LDAP or SSO).

Business Central allows the user to add new users/roles through the workbench but it only populates its own property files (hosted in the BC's image). Without LDAP or SSO Kie Server needs to know and have the same users/roles. So, we need a simple way to provide a list of users and its repective roles using the KieApp CR. So that the image can read from this list and persist them into the respective application-users.properties and application-roles.properties. 

Another alternative would be to allow the user to provide a ConfigMap with these two files. This way the image could get the users and roles from the config map.