Add option to ignore init-containers or specific container images.

This would be very useful so you can ignore for example k8s-wait-for init containers.

We use imago to update the actual service images the init containers are much less important and an update for k8s-wait-for causes everything to restart at once.

EDIT: Replacing init-container images does not seem to work at all, it keeps looping every iteration and restarting everything.