Kubernetes executor is not reinstating helper image ENTRYPOINT

In !2058 (merged) we added an ENTRYPOINT to the helper image that allows registering CA certificates if a file is found in a well known path (/etc/gitlab-runner/certs/ca.crt). Since the ENTRYPOINT instruction is discarded on a docker export operation, we've also added some code to the Docker executor behind a feature flag (FF_RESET_HELPER_IMAGE_ENTRYPOINT) to reset the ENTRYPOINT when we start a container.

This issue is about adding the same logic to the Kubernetes executor.

An alternative to this issue is relying on docker save instead of docker export.