esp_mqtt5_user_property_item_t struct

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

Get MQTT5 client user property This API can use with `esp_mqtt5_client_get_user_property_count` to get list count of user property. And malloc number of count item array memory to store the user property data. Please DO NOT forget the item memory, key and value point in item memory when get user property data successfully.