Monitoring grayskull support for R package recipes

[jdblischak]

Long-term the hope is that grayskull can replace these hacky scripts. The recent 2.0.0 release includes initial support for CRAN packages.

It shows potential, eg it already has a flag --strict-conda-forge, which was a long time dream of mine for conda skeleton cran, which instead was implemented piecemeal flag by flag. However, I don't think it's ready yet to replace these scripts. Most crucially, it doesn't yet handle the license files well, which is one of the main reasons these helper scripts have remained necessary over the years.

Implementation discussion in conda/grayskull#7, conda/grayskull#349, conda/grayskull#423

Current limitations: conda/grayskull#423 (comment), conda/grayskull#437