Need a way to know if image was actually rebuild

This a follow up of #7 (closed) so check it for the exact context.

I'd like to add to gstreamer-rs a "deploy" job executed at the end of the pipeline if all the previous job succeeded if and only if the "build image" job has actually generate a new image. This deploy job will trigger an image update to the plugins repo. It's not clear to me how to retrieve this information from the template.