Safer interrupt management demo for FreeRTOS kernel

FreeRTOS now contains an example code that demonstrates a method of minimizing the time an application spends in privileged mode in FreeRTOS ports on microcontrollers (MCU) with Memory Protection Unit (MPU) support. [FreeRTOS ports with MPU support](https://www.freertos.org/FreeRTOS-MPU-memory-protection-unit.html) enable MCU applications to be more robust and secure by running application tasks in unprivileged mode, where they have access only to their own stacks and pre-configured memory regions. The only application code that runs in privileged mode on these MPU enabled MCUs are Interrupt Service Routines (ISRs). The example code demonstrates an approach to keep ISRs short and defer most of the application work to unprivileged FreeRTOS tasks, which helps improve security of the application by minimizing the time it spends in privileged mode. To learn more and get started, visit the [demo page](https://freertos.org/safe-interrupt-demo-nxp-lpcxpresso55s69.html) and download the example code from the [Downloads page](https://freertos.org/a00104.html) or [GitHub](https://github.com/FreeRTOS/FreeRTOS).