Set the output to the output of the charmcraft CLI

[yhaliaw]

Enhancement Proposal

For actions such as upload-charm, charmcraft would output a JSON formatted message.
https://juju.is/docs/sdk/charmcraft-upload

Can the output of the action also have the output set to this JSON message?
https://github.com/canonical/charming-actions/blob/main/upload-charm/README.md

For my use case, I need to the error message from the charmcraft upload and process it in the next job step.
E.g.:

{
    "errors": [
        {
            "code": "review-error",
            "message": "Cannot insert package. An upload with that digest (SHA3-384: 'fdd098ab9c62a6b98fd3001201760b041197bf4c4114af0adf0f9f72ba0858f9da1a61cd654e0511f38f8c7d40c4[32](https://github.com/canonical/content-cache-operator/actions/runs/12722144608/job/35503821786#step:7:33)44') already exists in the database. Revision of the existing package is: 7"
        }
    ]
}