Auto-label in Invoke-DockerBuild

[rasmusjelsgaard]

The Invoke-DockerBuild cmdlet adds relevant labels to the images produced automatically on a best-effort basis. This is on top of whatever labels are added already in the Dockerfile.

The primary use case for this feature is from within CI/CD where the labels can be deduced.

It should be possible to manually override the labels and to add custom labels. The ability to add labels from a label file as well would be very handy in a CI/CD context.

https://github.com/opencontainers/image-spec/blob/master/annotations.md#pre-defined-annotation-keys provides a reasonable starting point. We should be able to deduce much of the information needed to provide these labels automatically.