RStudio image ignores pod environment variables

[IgorMilavec]

/kind bug

What steps did you take and what happened:
When I create an RStudio notebook, it does not take into account the environment variables specified through pod specification.
Images:
kubeflownotebookswg/rstudio-tidyverse:v1.7.0
kubeflownotebookswg/rstudio-tidyverse:v1.8.0

What did you expect to happen:
Envirnoment variables specified through pod to be set.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Kubeflow version: 1.7
• kfctl version: (use kfctl version):
• Kubernetes platform: EKS
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[thesuperzapper]

@IgorMilavec This is a known issue with RStudio, which we already partially work around for env-vars starting with KUBERNETES_... so that kubectl works:

See this file for more info about a possible workaround:

• https://github.com/kubeflow/kubeflow/blob/v1.8.0/components/example-notebook-servers/rstudio/s6/cont-init.d/02-rstudio-env-fix