Add RAIOT_MQTT library (#7404)

* Add RAIOTerm library

* Add RAIOT_MQTT library v1.0.0


- Added RAIOT_MQTT.h and .cpp source files
- Added library.properties with PubSubClient dependency
- Added Sender and Receiver examples
- Added LICENSE and README.md for RAIOTerm.cc integration

Author: Ultimate-raio01

repositories.txt

@@ -8726,5 +8726,6 @@ https://github.com/MR01Right/SHT40
 https://gitlab.com/Vishal1695/mvsota_esp32.git
 https://github.com/Glinek/omniMath
 https://github.com/raiotech-iot/RAIOTerm.git
+https://github.com/raiotech-iot/RAIOT_MQTT.git
 https://github.com/phirippa-source/RiaPushbuttonLite
 https://github.com/nbulatovi/Quecduino