feat: always return exit code 0

[Haegi]

Motivation

Right now the kube-fledged image cache jobs fail when pulled image fails to execute /tmp/bin/echo Image pulled successfully!. This is basically true for all container images without a shell like the distroless images.
Therefore, it is either not possible to use it with such images or to get a lot of failed jobs in the cluster.

This PR changes the behaviour to always return true and therefore exit code 0, which allows the usage of all images.

[samirgrl]

Thanks @Haegi — this is a thoughtful change. Returning exit code 0 from the cri-client after a successful pull makes the job lifecycle cleaner and avoids confusing operators who see non-zero exits in their logs even when nothing is wrong.

I've opened issue #242 to take over as maintainer. This PR would be on my review list early on. Do you have a test case to go along with it, or is the behavior observable from job status alone?

[senthilrch]

@Haegi Your proposal requires a shell in the container image. images without a shell would fail.