[WFLY-3591] Add keycloak auth to http management endpoint

This PR adds the ability to specify &lt;keycloak/&gt; as the authentication provider for the ManagementRealm in domain-http.  It does not actually pull any Keycloak artifacts into the target build.  On its own, this PR doesn't add any functionality in wildfly-core.  However, this is needed so that Keycloak can be added to wildfly full.
These deps aren't meant to be used as a single group.  This particular module depends on these, but different kinds of clients use different adapters.  For instance, a WAR would use the WildFly adapter instead of the pure Undertow adapter.  Also, the subsystem isn't closely related to the adapters and core could be used in lots of ways independently.