private static Endpoint defaultEndpoint(Server server) {
        final ServerPort serverPort = server.activePort();
        assert serverPort != null;
        return Endpoint.of(defaultAddress(server), serverPort.localAddress().getPort());
    }
Returns a {@link ZooKeeperUpdatingListenerBuilder} with a ZooKeeper connection string and a znode path.

@param zkConnectionStr the ZooKeeper connection string
@param znodePath the ZooKeeper node to register
@param spec the {@link ZooKeeperRegistrationSpec} to encode and register the {@link Server}
zookeeper3/src/main/java/com/linecorp/armeria/server/zookeeper/ZooKeeperUpdatingListener.java