@Override
    public ArmeriaResteasyClientBuilder defaultProxy(String hostname, int port) {
        delegate.defaultProxy(hostname, port);
        return this;
    }
{@link ArmeriaJaxrsClientEngine} will always be set as an {@link ClientHttpEngine}.
@throws UnsupportedOperationException always
resteasy/src/main/java/com/linecorp/armeria/client/resteasy/ArmeriaResteasyClientBuilder.java