Kubernetes executor ignores Docker ENTRYPOINT for the runner helper image

Release notes

The GitLab Runner Kubernetes executor build and helper image now honors entrypoint and works with exec "$@" which is typically used to make the entry point a passthrough to run the docker command.

Overview

In #4125 (closed) we addressed the issue with the Kubernetes executor ignoring Docker Entrypoint. However, as mentioned in this comment, we did not address the helper image.