[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.
Ok so the schema update should be minimal.

However the bit that worries me is I don't see how it could be appropriate for your changes to add a method for the 1.4 version of the schema, for your changes you should only be adding methods specific to version 3.0 of the schema.