Run demo in Ariel OS

[chrysn]

Currently, the best demos we have are in diondokter/nrf-modem#52.

Integrating with Ariel OS will work best on ariel-os/ariel-os#1328, and probably ariel-os/ariel-os#1398 rebased on that.

Then, we can more easily combine this with Teufelchen's slipmux implementation, and gain CoAP-over-WebSerial directly into the browser (incl. phones) for easy portable demos.

[chrysn]

Note that when using WebSerial (as may make sense for an early more usable RSSI-scanner/decoder demo), on the client side, mobile phones will need the polyfill integrated. (It does support WebSerial, it's just that it won't find USB devices).

The long-term solution for that kind of demos should be going through USB Ethernet; USB Serial as a starting point has the advantage that it can run on the Nordic devkits (because the onboard debugger forwards a serial port), and building the demo on CoAP means that application code can keep running across a switch on that.

[chrysn]

Side quest from here: Quickstart tutorial.