[docker-labels] Align with OCI image label spec

[aldeed]

The Open Container Initiative image spec lists label names and label value guidelines for Docker image labels:

https://github.com/opencontainers/image-spec/blob/master/annotations.md#pre-defined-annotation-keys

We should update the labels added by the docker-labels script to match this spec where they overlap. This will allow Reaction images to work well with third party tooling that expects such labels.