Add a way to query/install system dependencies of specific package

[thomasp85]

The system dependency query only works for a local package, making it hard to install remotes with any system dependencies. This surfaced as a user trying to install pkgdown which now requires ragg and hence it's slew of system libraries. It would be nice if there was a way to query dependencies by name so one wouldn't have to download the source package before making the query

something like install_github("pkgdown", system_dependencies =TRUE) would be amazing, but allowing remotes::system_requirements() to take a package name instead of a directory would be very good as well

[jimhester]

install_github("pkgdown", system_dependencies = TRUE) is impossible without some way to elevate permissions, since you generally need su access to install things from the package manager.

[thomasp85]

That was maybe also a pipe dream. But it would be nice to have some canned way of installing pkgdown on Linux with all the right system requirements