temp/megapixels-purism: new aport

This packages the megapixels fork that purism has supporting the librem 5.

I'm also not sure if I should be using replaces=megapixels here, I think maybe provides=megapixels might work but I don't want to end up causing apk to choose this package over the default megapixels in aports... and it's really easy to get it wrong and confuse apk. Alternatively I can just remove any replaces or provides...