avoid pushing artifacts without artifactType if --image-spec v1.1 is specified

[qweeah]

What is the version of your ORAS CLI

v1.2.0

What would you like to be added?

oras push supports pushing an artifact without artifactType even when OCI image spec v1.1 is specified.

➜  ~ oras push localhost:5000/artifact:type --format json --config <(echo -n "{}"):my/type --image-spec v1.1
✓ Exists    my/type                                                                                0/0  B 100.00%     0s
  └─ sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a
✓ Exists    application/vnd.oci.empty.v1+json                                                      2/2  B 100.00%     0s
  └─ sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a
✓ Uploaded  application/vnd.oci.image.manifest.v1+json                                         442/442  B 100.00%     0s
  └─ sha256:3179007d443a6c79a5e3b8af868cf762202ca3e95ecf87da456e59963913e006
{
  "Ref": "localhost:5000/artifact@sha256:3179007d443a6c79a5e3b8af868cf762202ca3e95ecf87da456e59963913e006",
  "MediaType": "application/vnd.oci.image.manifest.v1+json",
  "Digest": "sha256:3179007d443a6c79a5e3b8af868cf762202ca3e95ecf87da456e59963913e006",
  "Size": 442,
  "Annotations": {
    "org.opencontainers.image.created": "2024-03-28T01:43:28Z"
  },
  "ArtifactType": ""
}
➜  ~ oras manifest fetch --pretty localhost:5000/artifact:type
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "my/type",
    "digest": "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a",
    "size": 0
  },
  "layers": [
    {
      "mediaType": "application/vnd.oci.empty.v1+json",
      "digest": "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a",
      "size": 2,
      "data": "e30="
    }
  ],
  "annotations": {
    "org.opencontainers.image.created": "2024-03-28T01:43:28Z"

Why is this needed for ORAS?

According to the guidance, v1.1 artifact should always contains an artifactType, so

1. --config MUST not to be used with --image-spec v1.1 if --artifac-type is not specified, return error when encounter this.
2. --image-spec should be default to auto, which represents v1.0 if --config is used and --artifact-type not used. Otherwise v1.1

Are you willing to submit PRs to contribute to this feature?

• Yes, I am willing to implement it.

[wangxiaoxuan273]

I'd like to work on this issue

[qweeah]

--image-spec should be default to auto, which represents v1.0 if --config is used and --artifact-type not used. Otherwise v1.1

This is to make oras push --config xxx workable to avoid breaking change. Adding #1327 to remove this workaround in v2.0.