Draft: testing/py3-picamera2: new aport

using gpep517 as suggested by https://wiki.alpinelinux.org/wiki/APKBUILD_examples:Python

This works, e.g. with a program like https://git.sr.ht/~earboxer/picamera/tree/zachster/item/picamera.py to make a raspberry pi camera, powered by alpine... (actually the part which doesn't work is the gpio pins for the shutter button... but that's unrelated to the picamera2 library)

(draft until fix architecture-specific problems)