feat: show annotations in oras discover tree format output

[qweeah]

This PR enriches tree output of oras discover. Artifact annotations will be shown in yaml format if --verbose flag is set.

Resolves #631

$ IMAGE="localhost:5000/test:anno"
$ oras-demo push $IMAGE image
Uploading 254eddf15d95 image
Uploaded  254eddf15d95 image
Pushed localhost:5000/test:anno
Digest: sha256:93305aefab90f837c555e42afcce5a3d92e23180d5dc64e37363d78d65c93306
$ oras-demo attach $IMAGE sig -a "key: "="value ' " --artifact-type test.anno
Uploading 0a017e570e0b sig
Uploaded  0a017e570e0b sig
Attached to localhost:5000/test@sha256:93305aefab90f837c555e42afcce5a3d92e23180d5dc64e37363d78d65c93306
Digest: sha256:0f6ac3195806949d22ac6eaab804fa4fd5c25974acdfb003ddb4f24cc1b6da62
$ oras-demo attach $IMAGE -a "key"="value" --artifact-type test.anno
Uploading empty artifact
Attached to localhost:5000/test@sha256:93305aefab90f837c555e42afcce5a3d92e23180d5dc64e37363d78d65c93306
Digest: sha256:b9311291861ce206db11fdaf30a28492bac6a66b38b2183b17557cb49c7e18c2
$ oras-demo discover $IMAGE -o tree
localhost:5000/test:anno
└── test.anno
    ├── sha256:0f6ac3195806949d22ac6eaab804fa4fd5c25974acdfb003ddb4f24cc1b6da62
    └── sha256:b9311291861ce206db11fdaf30a28492bac6a66b38b2183b17557cb49c7e18c2
$ oras-demo discover $IMAGE -o tree -v
localhost:5000/test:anno
└── test.anno
    ├── sha256:0f6ac3195806949d22ac6eaab804fa4fd5c25974acdfb003ddb4f24cc1b6da62
    │   ├── 'key: ': 'value '' '
    │   └── org.opencontainers.image.created: "2023-01-09T02:24:17Z"
    └── sha256:b9311291861ce206db11fdaf30a28492bac6a66b38b2183b17557cb49c7e18c2
        ├── key: value
        └── org.opencontainers.image.created: "2023-01-09T02:24:37Z"

Signed-off-by: Billy Zha jinzha1@microsoft.com

[codecov-commenter]

Codecov Report

Merging #735 (53b96a5) into main (cdeca2f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #735   +/-   ##
=======================================
  Coverage   73.17%   73.17%           
=======================================
  Files          16       16           
  Lines         574      574           
=======================================
  Hits          420      420           
  Misses        123      123           
  Partials       31       31           

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[shizhMSFT]

Will <key>: <value> better than <key> = <value>?

[qweeah]

Will <key>: <value> better than <key> = <value>?

What's the intention of using colon? If it's for automation, then json output is definitely a better option. Since annotation key can contain a colon. If we use colon we'd better double quotes the key and value, with double quotes escaped. E.g. showing "my:key" : "my\\":value" for sha256:7b2b5d

$ oras-demo attach localhost:5000/test:anno -a "my:key"="my\":value" --artifact-type test.more
$ oras-demo attach locadiscover localhost:5000/test:anno -o tree
localhost:5000/test:anno
├── test
│   └── sha256:df31b7792e0f0d3bffa5843da07bfd7ab27c1ec756c37c5c55c56eaf44f3f636
│       └── org.opencontainers.image.created = 2023-01-05T09:08:01Z
└── test.more
    ├── sha256:d6e7f841cca49f4bb90f3f3a96183269f6b00a3eae87f9b1cd7655feb8a8d2f0
    │   ├── org.opencontainers.image.created = 2023-01-05T15:16:31Z
    │   ├── test = 123
    │   └── test2 = 456
    └── sha256:7b2b5d28bde095f2949fb62af5a75d05f1e9e7d0f80f2eab12b44ecd79f13442
        ├── my:key = my":value
        └── org.opencontainers.image.created = 2023-01-06T04:11:47Z

cc @yizha1 @FeynmanZhou

[shizhMSFT]

What's the intention of using colon?

It is for human readability. Basically, <key>: <value> format is YAML like.

[shizhMSFT]

What's the reason to trim space?

[qweeah]

1. yaml.Marshal will add a new line automatically at the end of any object, which makes the tree view less prettified
   

2. Heading/trailing spaces in key/value will be quoted by yaml.Marshal, thus trimming space will not cause unwanted change to annotation key/value

[shizhMSFT]

Sounds good.

[shizhMSFT]

LGTM