Adding ESP32 core selection for MQTT task

[vtunr]

Since we can run FreeRTOS on both core, it is interesting to be able to pin MQTT task to one core.

In order to do that, I added one parameter and two choices in KConfig :

• MQTT_TASK_CORE_SELECTION_ENABLED
• MQTT_USE_CORE_0

• MQTT_USE_CORE_1

  Then it use xTaskCreatePinnedToCore if the option is used.

[vtunr]

@tuanpmt I updated according to your remarks, I hope everything is ok now :)