[Feature Request] Add `name`, `version`, `arch` and any other useful metadata as outputs of `rockcraft-pack-action`

[ca-scribner]

The rockcraft-pack-action provides an output rock (the filename of the rock produced). This is great for CI as reduces the boilerplate code needed to consume the output.

For the same reason, it would be great if this action also provided data like name, version, and probably others. This would make it really easy to chain a rockcraft-pack call with a skopeo copy, etc. A use can currently inspect the rockcraft.yaml file to get this information, but it feels more natural and convenient to be provided these directly from rockcraft-pack-action