RStudio resources

[abkfenris]

This issue comment was the most useful for getting RStudio up and running: https://github.com/jupyterhub/zero-to-jupyterhub-k8s/issues/990#issuecomment-559598856

Also explored setting up a new profile:

• https://github.com/jupyterhub/jupyter-rsession-proxy/issues/93
• https://github.com/riazarbi/k8s_setup/blob/master/configure_sandbox.sh#L48-L53
• https://github.com/jupyterhub/jupyter-rsession-proxy/issues/73