Adds multiple image save to tarfile.

[jglogan]

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Description

% container image save -o container.tar python:alpine alpine:latest
Warning! Running debug build. Performance may be degraded.
Image(s) saved        

% tar tf container.tar 
oci-layout
blobs/
blobs/sha256/
blobs/sha256/02f8efbefad605a169e89926147edd0676646263268f303c6fb3cdfdbc4a9612
blobs/sha256/a4bb08daca6b0385b17761b170fc91b20ab2ec072f70f9260149f8d61846ac13
blobs/sha256/588270f913bc82b4dbeee27bc249e4d314894becd18cccdc13645f669972c91e
blobs/sha256/692b7bac6678f5809640189eb1d95a3277689ec643201c465ecd44e72db7d029
blobs/sha256/1d24a57b1de9b287d9a9e1e231b71a235b836dc1852155b943b927a411d8c394
blobs/sha256/f9841e55dcbf5a6fcc702b25ce6e411ebdcb30680f94afd8060cb20bb20bd75c
blobs/sha256/0b83d017db6efafadf6b3f18d087d2ce1d67d8f0e927dc7254b0ad088074cd3a
blobs/sha256/b2236d9e1563c507613962c1ebbd7b3d307969ec2ee355b781b68440f4f0bee3
blobs/sha256/6e174226ea690ced550e5641249a412cdbefd2d09871f3e64ab52137a54ba606
blobs/sha256/c879780ac011609647c8714eef9e6490c42bf20128b32f4b31c4daad1242647b
blobs/sha256/26a1da51444d4cbbba3233caa342d0397ac4f93dc8e305e31989fd782b3107da
index.json

% tar -xOf container.tar index.json | python3 -m json.tool
{
    "schemaVersion": 2,
    "mediaType": "application/vnd.oci.image.index.v1+json",
    "manifests": [
        {
            "mediaType": "application/vnd.oci.image.index.v1+json",
            "annotations": {
                "org.opencontainers.image.ref.name": "docker.io/library/python:alpine",
                "io.containerd.image.name": "docker.io/library/python:alpine",
                "com.apple.containerization.image.name": "docker.io/library/python:alpine"
            },
            "size": 944,
            "digest": "sha256:1d24a57b1de9b287d9a9e1e231b71a235b836dc1852155b943b927a411d8c394"
        },
        {
            "mediaType": "application/vnd.oci.image.index.v1+json",
            "annotations": {
                "io.containerd.image.name": "docker.io/library/alpine:latest",
                "org.opencontainers.image.ref.name": "docker.io/library/alpine:latest",
                "com.apple.containerization.image.name": "docker.io/library/alpine:latest"
            },
            "size": 497,
            "digest": "sha256:692b7bac6678f5809640189eb1d95a3277689ec643201c465ecd44e72db7d029"
        }
    ]
}

Motivation and Context

image load can read multiple images from a tar file, but image save cannot save multiple images today.

Testing

• Tested locally
• Added/updated tests (TODO: roundtrip test pull-save-rm-load)
• Added/updated docs (TODO: check command reference)

[katiewasnothere]

could we add the list of images that failed to this message?

[katiewasnothere]

Closes #558