build: add ci to check that that all artifacts exist

Adding ci in response to issue that I caused yesterday where I made a typo in one of the image tags that broke the replication workflow. ci iterates over all images and helm charts to verify that they exist using skopeo inspect (which only pulls image manifest) or helm show chart.

Using this was able to catch two images that were referencing to the now deprecated and frozen k8s.gcr.io registry.