public MirrorClientConfig clientConfig(String cluster) {
        Map<String, String> props = new HashMap<>();
        props.putAll(originalsStrings());
        props.putAll(clusterProps(cluster));
        return new MirrorClientConfig(transform(props));
    }
Construct a MirrorClientConfig from properties of the form cluster.x.y.z.
Use to connect to a cluster based on the MirrorMaker top-level config file.
connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorMakerConfig.java