improve error log for oras push and oras attach when annotation file is invalid #1021
Description
If a malformed JSON file is provided via --annotation-file flag, oras will output below error log, which is hard to understand for the common user.
Error: json: cannot unmarshal string into Go value of type map[string]string
CLI should
- give hints of the provided path of JSON file is malformed, and
- point user to the document in https://oras.land/docs/how_to_guides/manifest_annotations.