The API of FreeRTOS/backoffAlgorithm library has changed to remove dependency on random number generator; instead require the caller to generate the random number and pass it to the BackoffAlgorithm_GetNextBackoff API for backoff period calculation. This PR updates the submodule pointer commit, and updates the demos and tests to use the simplied library API
A new repository, FreeRTOS/backoffAlgorithm, has been created for hosting the library for backoff calculation. This repo replaces the FreeRTOS-Plus/Source/Utilities/exponential_backoff with the submodule to the new repository, and updates all the demos that use retry logic to use the backoffAlgorithm API
* Add submodule pointer to the aws/jobs-for-aws-iot-embedded-sdk repository for the Jobs library
* Commonize the MQTT helper functions used by the Device Shadow demo by re-locating them to FreeRTOS-Plus/Demo/AWS/MQTT_Demo_Helpers and updating the Device Shadow demo to use the new files
