Function esp_mqtt5_client_set_user_property 

pub unsafe extern "C" fn esp_mqtt5_client_set_user_property(
    user_property: *mut *mut mqtt5_user_property_list_t,
    item: *mut esp_mqtt5_user_property_item_t,
    item_num: u8,
) -> i32

@brief Set MQTT5 client user property configuration

This API will allocate memory for user_property, please DO NOT forget call esp_mqtt5_client_delete_user_property after you use it. Before publish data, subscribe topic, unsubscribe, etc, call this API to set user property if have

@param user_property user_property handle @param item array of user property data (eg. {{“var”,“val”},{“other”,“2”}}) @param item_num number of items in user property data

@return ESP_ERR_NO_MEM if failed to allocate ESP_FAIL on fail ESP_OK on success