[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.
Actually the file has been added, just called wildfly_config_3_0.xsd

As you are only adding a single element to the <authentication /> element the only new method you need to add is the parseAuthentication_3_0().

At every point an <authentication> element could be added during parsing an appropriate switch statement needs to be added based on the namespace version.  However keep in mind that each of those methods is only applicable for a subset of supported schema versions so each does not need to contain an exhaustive list of versions.