* [CI] Move lint to a separate script
* [CI] Improved lintr launcher
* Add lintr as a separate action
* Add custom parsing logic to print out logs
* Fix lintr issues in demos
* Run R demos
* Fix CRAN checks
* Install XGBoost into R env before running lintr
* Install devtools (needed to run demos)
* [R-package] replace uses of T and F with TRUE and FALSE
* enable linting
* Remove skip
Co-authored-by: Philip Hyunsu Cho <chohyu01@cs.washington.edu>