Document the Kubernetes back-end deployment

[chrisdoherty4]

We've introduced a Kubernetes back-end and some maintainers have written compose files to get up and running (unmerged). We need to define a clear path for deploying with the Kubernetes back-end, then document it

[chrisdoherty4]

Some strides have been made with updates to the sandbox. We also have a documentation effort on the roadmap tracked by the Documentation Updates project.