public <S, Q> S postGateway(final String path, final Type respType) throws IOException {
        return postGateway(path, "", respType);
    }
Send a post http request to shenyu gateway.

@param <S>      type of response object
@param <Q>      type of request object
@param path     path
@param respType response type passed to {@link Gson#fromJson(String, Type)}
@return response s
@throws IOException IO exception
shenyu-integrated-test/shenyu-integrated-test-common/src/main/java/org/apache/shenyu/integratedtest/common/helper/HttpHelper.java