Use Raspberry Pi and Pi Cam for Prusa Connect

I couldn't get the script from p123ad to work on my Pi Zero W 2 with Camera Module 3 (all kinds of ffmpeg errors). There are several built-in tools for working with the camera now, so I tried to figure out if I could use one of those instead.

Behold this version, which uses the built-in libcamera-still tool to actually interact with the camera and save a JPEG. That image is then uploaded to Prusa Connect, same as the original script.