Docker plugin fails for images using oci v1 media types #71

Any images that still use application/vnd.oci.image.manifest.v1+json and/or application/vnd.oci.image.layer.v1.tar+gzip (such as library/archlinux on docker hub) cause the docker plugin to error with a 404 error code, even though the image definetly exists.

Manually adding these two media types to the relevant mediaType checks and accept headers makes it work reliably for pretty much every plugin that I tested.