diffoci mediatype

[mzihlmann]

diffoci is the tool we use for integration tests. For example we build the same image once with buildkit and once with kaniko and diff the resulting images with that tool. As the name implies diffoci works on oci images and only on oci images. If presented with a dockerv2 image it will first convert the image to ociv1 type and then perform the diff. This leads to some awkward situations as 1. kaniko can wrongly emit the wrong mediatype and we don't notice, and 2. some features are mediatype specific, ie. ONBUILD only exists in dockerv2, so a diff on those features cannot be detected. My thinking is to extend diffoci to support different mediatypes and no longer force a conversion? This would make the name a bit misleading at that point but whatever. Alternatively we could look for different tooling that supports a more strict diffing, not sure if any exist? What's your take?