support a way to verify that all images are preresolved

**Describe the problem/challenge you have**

when applying a lock file that preresolves all images, it may be useful to verify that all found images by kbld have indeed been preresolved by the config. this would help finding problematic config (of images) before they get deployed to the cluster and potentially cannot be downloaded.

**Describe the solution you'd like**

add optional `--expect-all-preresolved=bool` flag (default false). can it be noun-ized further?

**Anything else you would like to add:**

n/a