Allow installing a local `.pkg` or `.tar.gz` or `.msi` file

[gaborcsardi]

With rim add <filename> as usual.

[gaborcsardi]

For macOS, we would need to extract the R version from the .pkg file, with something like

pkgutil --bom R-4.1.2.pkg
lsbom /tmp/R-4.1.2.pkg.boms.ZOFdZ8/R-fw.pkg/Bom