## What changes were proposed in this pull request?

(Please fill in changes proposed in this fix)

## How was this patch tested?

This change adds CRAN documentation checks to be run as a part of `R/run-tests.sh` . As this script is also used by Jenkins this means that we will get documentation checks on every PR going forward.

(If this patch involves UI changes, please attach a screenshot; otherwise, remove this)

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #14759 from shivaram/sparkr-cran-jenkins.