Support OCI Registry For Code Upload

[manno]

The current implementation uploads the user's code to an S3-compatible object store, i.e. minio.

OCI registries support arbitrary data.
This could allow Epinio to drop minio and use the same registry for source code and images.

The main problem seems to be that dockerhub doesn’t support the media type. Epinio could use a, OCI spec-breaking, workaround, like cosign does.

There are go libraries to deal with uploading and downloading.

If Epinio wants to have more plugability, it could support both S3 and OCI registries. When running locally, e.g. Rancher Desktop the OCI registry might be sufficient. Large production deployments probably want to use S3.

• Do we need to support all registries?
• How ephemeral are the code blobs?