Content Negotiation does not match implementation behavior

[sudo-bmitch]

We currently have https://github.com/opencontainers/distribution-spec/blob/v1.1.1/content-negotiation.md

This doesn't match the behavior of some popular implementations, and there's also a desire to remove support for Docker's v1 manifest. I think we should either rebuild this table or remove it entirely. If we rebuild it, I'd like to see it allow clients to request any content with an Accept /, or no Accept header at all. And otherwise, I think we could significantly simplify it since OCI only defines two manifest media types, so there could be optional logic to select a manifest from an index (first entry, or a well known platform?).

If we remove the page, it would be good to point to a HTTP RFC on Accept/Content-Type headers (I believe that's 7231 section 5.3.2 and section 3.1.1.5) and then we need to decide if we lose the ability to return an image manifest from an index.

[sudo-bmitch]

To capture the comments in today's meeting, there's a desire to remove the file and not have any support for having the registry return a manifest from within an index in future versions of the spec. Registry support for the Accept header is going to vary, so if we include that, I think it would be limited to "MAY" language.