Define configASSERT() macro in FreeRTOSConfig.h

[escherstair]

Based on the official documentation here and on the FreeRTOSConfig.h template supplied here https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/3a7b3082cfce01ffba07b9be1398795b8307b05a/examples/template_configuration/FreeRTOSConfig.h#L410-L424

FreeRTOSConfig.h should contain a definiton of configASSERT() macro, to trap errors during development. I always have to remember to add this.

Can you provide this directly in this repo?