Provide a documentation for Elytron WildFly Security Manager, its configuration options and the subsystem.

Pick up the information out of

• https://wildfly.zulipchat.com/#narrow/stream/173102-wildfly-elytron/topic/Protection.20Domains
• https://www.redhat.com/en/blog/harden-your-jboss-eap-71-deployments-java-security-manager
• https://github.com/wildfly-security/wildfly-elytron/blob/1.x/manager/base/src/main/java/org/wildfly/security/manager/WildFlySecurityManager.java