Add docs about non-root jobs in Kubernetes
What does this MR do?
Documents settings to use in non-root jobs or if FF_DISABLE_UMASK_FOR_KUBERNETES_EXECUTOR=true.
I tested this with Operator into our Kubernetes cluster. I've hit such errors before when trying to run non-root jobs and Runners with custom ConfigMap & SCC fail chown ... (gitlab-org/gl-openshift/gitlab-runner-operator#246 - closed) • Georgi N. Georgiev | GitLab • 18.4 prompted me to dig deeper.
These issues are mentioned in the original MR - Change directories and files permissions for ba... (!5415 - merged) • Romuald Atchadé - OOO until Nov 30th, 2025 • 17.11 but never fixed or documented.
I don't even think we tested this into our cluster in the end, which we should have, so we could at least add docs.