Use custom media types for request and responses

[stevvooe]

Custom media types will make it easier for us to iterate on request and response formats for API methods. It will also make migrating to new formats and maintaining backward compatibility much more straightforward.

Implementation plan:

1. Experiment with media types in webhook implementation Webhook notifications #42. For this, we'll try to use application/vnd.docker.distribution.events.v1+json for the event format.
2. Set baseline use of application/json to refer to the current specification.
3. Define custom media types for other formats (manifest, layers, etc.). Here are some possible examples:
   • Layer: application/vnd.docker.distribution.layer+tar
   • Manifest: application/vnd.docker.distribution.manifest.v1+json
   • Signed Manifest: application/vnd.docker.distribution.manifest.v1+prettyjws

[dmcgowan]

Discussion now a part of OCI artifacts spec