bug#47525: docker layer DiffID incorrect

[Tom Hiller]

The Docker image created using "guix pack -f Docker" generates the sha256 checksum of config.json as the layer diff id used in manifiest.json, repositories and the parent directory name of layer.tar.  When extracting the contents of the Docker image, the sha256 checksum of config.json does not match the used for the layer.  As Docker currently does not seem to verify this, the image will still work but may not always be the case.

I am not familiar with Guile Scheme, but as best as I can determine in guix/gnu/services/docker.scm the checksum calculated in layer-diff-id is the of Scheme native. and not the ultimate JSON document.