Setting up the home directory in Kubernetes

Just as a followup to my question about how kubernetes mounts volume, indeed it doesn't seem possible to use overlay mount to preserve pre-existing files in the `/home/jovyan` directory in the image. I found this StackOverflow answer interesting. https://stackoverflow.com/a/63128564/3682277

> A common solution for your use-case is, to use an init container to set up the [emptyDir](https://kubernetes.io/docs/concepts/storage/volumes/#emptydir), before the main container is started. So basically you specify the emptyDir as a volume mount in both the init container and the main container and have the init container copy the files into the emptyDir.

Might be interesting to explore, in case you haven't already CC @unkcpz @superstar54

In any case, whatever solution you arrive at at the end, we should document it somewhere in this repo.