topic_t struct

Subscribe the client to a list of defined topics with defined qos Notes: - Client must be connected to send subscribe message - This API is could be executed from a user task or from a *MQTT* event callback i.e. internal *MQTT* task (API is protected by internal mutex, so it might block if a longer data receive operation is in progress. - `esp_mqtt_client_subscribe` could be used to call this function.