Built-in image copy mechanism (skopeo replacement)

[estahn]

k8s-image-swapper is currently using skopeo, a CLI, to copy images into the registry. This is being executed as an external command and can lead to several issues (OOM, security exposure via skopeo, ...).

skopeo is utilising github.com/containers/image/v5/copy, with some added mechanics like retry, which can be utilised directly in k8s-image-swapper.