Flag a warning in the debug logs if the customer is using unsupported hardware

[mtlynch]

Sometimes, customers file support requests saying that TinyPilot doesn't work on their device, and it takes a few back-and-forths to discover that they're running it on unsupported hardware.

We should flag a warning in the debug logs if we detect that the running hardware does not match compatible hardware (Pi 4B or Pi Zero series). Only Pi 4B is officially supported, but Pi Zero should also at least work out of the box.

Depends on #228