Add CI to automatically generate changelog for image releases

It would be very helpful to have a CI that automatically generates a changelog for new image releases, similar to what is already available in [atomic-desktop](https://github.com/AlmaLinux/atomic-desktop/releases
).

I think the best approach would be to generate and publish an SBOM (probably using Syft) for each release, so that could be reused for other purposes as well. But simply using the rpm command to generate a package diff should be sufficient as a starting point.