feat(pico-sensor): added callback in mqtt client to process incomming messages in application

pico-sensor/src/mqtt_client.h

@@ -70,6 +70,32 @@ void MqttClient_Deinit(void);
  */
 void MqttClient_Init(void);
 
+typedef enum topic_ID_e {
+  Topic_ID_None,
+#if MQTT_CLIENT_IS_EV_CHARGER
+  Topic_ID_Solar_Power,       /* power from PV panels */
+  Topic_ID_Site_Power,        /* power to the house/site */
+  Topic_ID_Grid_Power,        /* power from/to grid */
+  Topic_ID_Battery_Power,     /* power from/to battery */
+  Topic_ID_Battery_Percentage,/* battery level percentage */
+  Topic_ID_Charging_Power,     /* actual charging power */
+#elif MQTT_CLIENT_IS_SENSOR
+  Topic_ID_Sensor_Update,
+#endif
+} topic_ID_e;
+
+/*!
+ * \brief Callback function for incoming messages
+ */
+typedef void (*MqttClient_MessageCallback_t)(topic_ID_e topic, const unsigned char *payload, size_t len);
+
+/*!
+ * \brief Register a callback function for incoming messages
+ * \param cb Callback function to be registered
+ */
+void MqttClient_RegisterMessageCallback(MqttClient_MessageCallback_t cb);
+
+
 #ifdef __cplusplus
 }  /* extern "C" */
 #endif