Use OCI mediaTypes

[lcarva]

Feature request

It should be possible to use the tkn bundle push command to generate an Image Manifest with the OCI media type. Since these bundle images are not traditional container images, let's consider using artifactType.

Use case

The OCI standard clearly defines how artifacts should be described in an OCI registry. The docker media types do not. This is about more accurately representing the content.

UI Example

Ideally, by default the updated tkn bundle push command pushes an OCI artifact to the registry. A flag, e.g. --legacy, could be added if necessary to produce a docker image manifest.

(The command is marked as experimental, so maybe we don't have to worry about legacy behavior.)