[MINOR][R] Add knitr and rmarkdown packages/improve output for version info in AppVeyor tests#18336

HyukjinKwon wants to merge 3 commits intoapache:masterapache/spark:masterfrom

HyukjinKwon:minor-add-knitr-and-rmarkdownHyukjinKwon/spark:minor-add-knitr-and-rmarkdownCopy head branch name to clipboard