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 Just decided to disable the arches that fail tests... can come back to them later, this is "testing" after all.)

Draft until some versions are bumped...