Review RTOS options for running ESP32 radios

[tcr]

This probably falls into the category of "use what's in the dev kit", but: We should determine what OS the ESP32 needs to run in order to meet Reach's criteria.

In the past (see the SAMD21 running on T2) we've used a self-written firmware that runs directly on the metal to power our hardware applications. We also (in the T1) have integrated with Wifi radio event loops in a bare metal environment. FreeRTOS, which the esp-idf ships with, is higher level than what we've worked with before, and represents a set of trade-offs we should be explicit about. If the alternative is to run a bare-metal firmware, or an alternative RTOS like NuttX, etc. we want to pick the best tool for the job.

TODO:

• Determine if the ESP32 requires the FreeRTOS stack to power its radio stack
• See if bare-metal code examples running on the ESP32 exist
• Create a tradeoffs list for each of our options and select a path forward for A) prototyping and B) production (these may be different)