r: Bump to 4.0, use older RStudio
r: Bump to 4.0, use older RStudio

Newer RStudio has issues with jupyter-server-proxy
and won't work yet. But we want newer R, partially so
we can get newer packages. So this gets us there.

See https://github.com/berkeley-dsep-infra/datahub/pull/1666
and the reverts that follow

berkeley-dsep-infra/datahub,ryanlovett/datahub,ryanlovett/datahub,berkeley-dsep-infra/datahub,ryanlovett/datahub,berkeley-dsep-infra/datahub