Move package_sets.yaml into the data directory.

[supakeen]

Currently the package_sets.yaml live inside pkg/distro/${name}/package_sets.yaml. Can we move them to data/definitions/${name}/package_sets.yaml?

This would enable us to ship them in the same way we ship repositories where we can 'overlay' a data directory from image-builder. Having this would allow us to start experimenting with building Fedora with adjusted package sets.

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Note: I'd prefer the path to be: data/definitions/${distro}/packages/${image-type}.yaml and to drop the main key. I'm not suggesting that as the first iteration as there's currently a lot of deduplication happening within that single file.

[bcl]

I like this idea.