Add support for inspecting signatures on a reference

[byronchien]

Adds support for notation inspect (spec here)

Example output:

chienb@a07817b52895 notation % ./bin/notation inspect $IMAGE
Resolved artifact tag `v1` to digest `sha256:5a07385af4e6b6af81b0ebfd435aedccdfa3507f0609c658209e1aba57159b2b` before inspect.
Warning: The resolved digest may not point to the same signed artifact, since tags are mutable.
Inspecting all signatures for signed artifact
localhost:5000/net-monitor@sha256:5a07385af4e6b6af81b0ebfd435aedccdfa3507f0609c658209e1aba57159b2b
└── application/vnd.cncf.notary.signature
    └── sha256:34e5843a1a8b1607d2ba7da9b61c6a5b3953f5680751c160fb944df87b01b2b2
        ├── signature algorithm : RSASSA-PSS-SHA-256
        ├── signed attributes
        │   ├── expiry : 0001-01-01 00:00:00 +0000 UTC
        │   ├── signingScheme : notary.x509
        │   └── signingTime : 2023-01-27 17:02:22 -0800 PST
        ├── user defined attributes
        │   └── io.wabbit-networks.buildId : 123
        ├── unsigned attributes
        │   └── signingAgent : Notation/1.0.0
        ├── certificates
        │   └── SHA1 fingerprint e1ef7b0f984d1f8222d6bf297e1ad10047997b54
        │       ├── issued to : CN=byron.test,O=Notary,L=Seattle,ST=WA,C=US
        │       ├── issued by : CN=byron.test,O=Notary,L=Seattle,ST=WA,C=US
        │       └── expiry : 2023-01-29 01:02:13 +0000 UTC
        └── signed artifact
            ├── media type : application/vnd.docker.distribution.manifest.v2+json
            ├── digest : sha256:5a07385af4e6b6af81b0ebfd435aedccdfa3507f0609c658209e1aba57159b2b
            └── size : 942
chienb@a07817b52895 notation % ./bin/notation inspect $IMAGE --output json
{
    "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
    "Signatures": [
        {
            "digest": "sha256:34e5843a1a8b1607d2ba7da9b61c6a5b3953f5680751c160fb944df87b01b2b2",
            "signatureAlgorithm": "RSASSA-PSS-SHA-256",
            "signedAttributes": {
                "expiry": "0001-01-01 00:00:00 +0000 UTC",
                "signingScheme": "notary.x509",
                "signingTime": "2023-01-27 17:02:22 -0800 PST"
            },
            "userDefinedAttributes": {
                "io.wabbit-networks.buildId": "123"
            },
            "unsignedAttributes": {
                "signingAgent": "Notation/1.0.0"
            },
            "certificates": [
                {
                    "SHA1Fingerprint": "e1ef7b0f984d1f8222d6bf297e1ad10047997b54",
                    "issuedTo": "CN=byron.test,O=Notary,L=Seattle,ST=WA,C=US",
                    "issuedBy": "CN=byron.test,O=Notary,L=Seattle,ST=WA,C=US",
                    "expiry": "2023-01-29 01:02:13 +0000 UTC"
                }
            ],
            "signedArtifact": {
                "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
                "digest": "sha256:5a07385af4e6b6af81b0ebfd435aedccdfa3507f0609c658209e1aba57159b2b",
                "size": 942
            }
        }
    ]
}

Signed-off-by: Byron Chien chienb@amazon.com

[byronchien]

TODOs:

• Add a generic tree printer, would ideally like to just do a printObjectAsTree(foo) instead of all the plaintext print logic
• update verify to use the getDescriptorFromPayload instead of the metadata specific helper