Support local OCI base images

[TadCordle]

Right now, Jib only supports Docker daemon images and Docker-formatted tars locally. As a follow-up to #2124, it'd be good to allow Jib to use local OCI base images. We may re-use the tar:// prefix and automatically infer the format, or introduce a new oci:// prefix since OCI archives can simply be exist in a directory structure rather than in a tar.