Message if R version is outdated

[gaborcsardi]

Ideally, it would only warn if a binary installer is available for the platform, and only once per session. It probably should not warn on the CIs, and in Docker.

[jimhester]

Probably only for interactive sessions as well?

[gaborcsardi]

I thought about that, but where is the harm in doing it for non-interactive sessions? pkgman will already print messages about the packages to be installed, etc.

[jimhester]

I guess maybe none, but I was thinking about if people have a task running R on a server and would get worried if there was a warning showing up in the logs.

But I guess this would only be during installation, so it is probably fine.

[gaborcsardi]

Technically it would not be a warning, just a message. Sorry, the issue title is confusing.

We would also add an env var to suppress it. pkgman will probably have a non-interactive deployment mode, similar to npm ci, and there we would not show the "warning".