registry: Change the way in which images are tagged

registry: Change the way in which images are tagged

Previously we tried using the git commit ref as a UID for the
images. This does not work though cause multiple jobs that rebuild
the image can be triggered and override the same image tag. Instead
use the CI_JOB_ID to provide better semantics wrt naming conflicts.

Additionally add the date as part of the tag to better indicate
the age of the image. Gitlab WEBGUI doens't indicate the age
in a good way nor makes it easy to short the images.