Currently osbuild/images assume the container is in local storage and therefore uses containers-storage source. Make this configurable behavior, when a new flag "local" set to false, it would use skopeo source to download the container.

This means the osbuild command on worker is self-sufficient and it can download all data, then we can tar it and copy to the executor like we do currently. No changes necessary.

Make sure this option can be configured via runtime configuration, we will set this flag to false for insights cluster.

The local storage field already exists in images, we just need to expose it so composer can use it and create a config option: https://github.com/osbuild/images/blob/7328a3efc2b79ed6a84bee5bdf18add18d07f13c/pkg/osbuild/source.go#L156-L166