Add instructions to `k8s-gitlab.md` for working with the new `gitlab-helmfiles` repo
As we are in the process of migrating and merging repos under k8s-workloads
into
a single gitlab-helmfiles
repo, we need to update this document to reference
its inclusion and the steps to use it.
This is an initial addition, and will be further refactored as more workloads are migrated.
Edited by Graeme Gillies