Over time unless they're removed, the project could grow quite a large
collection of VM images. While generally cheap (less than a penny each,
per month), these will become a significant cost item if not kept
in-check.
Add a specialized container for handling image-pruning, but limit
it to only finding and printing (not actually deleting) images.
Also update the image-building workflow so that base-images used to
compose cache-images are also labeled with metadata.
N/B: As an additional safeguard, the service account which
executes the new container in production *DOES NOT*
have access to delete images. This can be enabled
by adding the GCE IAM role: CustomComputeImagePrune
Signed-off-by: Chris Evich <cevich@redhat.com>
