Add qemu-x86_64 image to storage.puri.sm

By storing the qemu-x86_64 image to some place on storage.puri.sm, we could direct users to a cleaner link that is not some jenkins build link.

I would like to see a latest tested image in https://storage.puri.sm/librem5/binaries/unstable/latest/ and I would be happy to periodically manually update this image to a new tested one.

I prefer the latest folder to https://storage.puri.sm/librem5/binaries/ci/ because it is a pain to have to frequently go and clean out old images. There are already plenty of old images for uboot and the kernel. If we add the qemu-x86_64 images to this, then the folder will fill up even quicker and it will become obvious that someone needs to go remove old images only when there is no space left.