add reference details to output errors

[qweeah]

What is the version of your ORAS CLI

oras 1.1.0

What would you like to be added?

Some oras commands like oras copy, oras discover and oras attach require user to specify a tag or digest. If not provided, oras would output error information like:

invalid image reference, expecting name:tag|name@digest

oras should output more specific error info like:

no tag or digest when expecting name:tag|name@digest

Why is this needed for ORAS?

It would make error message more friendly to newbie users who are not familiar with concepts like image reference.

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

• Yes, I am willing to implement it.

[qweeah]

#1152 solves this for remote registry targets, extra work need to be done for OCI layout targets.

[FeynmanZhou]

Could you change the issue title to add reference details to error messages for OCI layout and registry? I think the major intention of this issue is to improve the error messages for OCI layout as well as some cases that across two targets.