[FEATURE] Support OCI Artifact Source Created by `oras`

[adambkaplan]

Is there an existing feature request for this?

• I have searched the existing feature requests

Is your feature request related to a problem or use-case? Please describe.

ORAS is a popular utility for creating OCI artifacts from raw files. It does not require a Dockerfile or similar instruction set to package a set of files in "scratch" container images. Just give it a set of files, or an entire directory, and it works!

Describe the solution that you would like.

Support local source code created by ORAS as an OCI source. A few things to note:

1. ORAS images default to an artifact type of application/vnd.unknown.artifact.v1. This can be configurable.
2. When uploading directories, the layer media type is application/vnd.oci.image.layer.v1.tar+gzip
3. ORAS file layers can have arbitrary MIME types - this is configurable by the user.

Describe alternatives you have considered.

Explicitly restrict OCI source to support content created by "scratch" Dockerfile/Containerfile builds.

Anything else?

More info on how ORAS works: https://oras.land/docs/how_to_guides/pushing_and_pulling