Support formatted JSON output for oras copy

[FeynmanZhou]

What is the version of your ORAS CLI

ORAS v1.1.0

What would you like to be added?

When writing the feature spec ORAS formatted output, the --format flag is not considered in oras copy because its scenario is not common and clear enough.

We do see users want to find out all the referrers that did get copied and their digest and artifactType that got copied over in the output. But this feature request has not been justified as a common scenario in the community and can even be achieved by using formatted JSON output of oras discover.

This issue is created for gathering more potential use cases of using formatted JSON output with oras copy. If you have any requirements or scenarios related to this feature request, feel free to comment on this issue.

Why is this needed for ORAS?

N/A

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

• Yes, I am willing to implement it.