GH-16360: Fix R package for Windows

[tomasfryda]

#16360

The Windows usually don't allow opening one file by multiple processes and that seems to cause this issue.

In python, it seems like we are using the same process group which IIRC could mitigate the issue we're seeing in R.

Last time I programmed on Windows, Delphi was a big thing and Windows XP was the latest version so my knowledge of that "operating system" is pretty limited. So I'm trying to keep it simple and multiplatform without delving into windows' and R's internals.

My solution is to add the web_ip to the json we send when H2O connects and then check on R side if it's null and if so print the warning. This way we print it every time on h2o.init and also on h2o.connect (which I think is a good thing) but it makes the behavior between R and Python diverge a bit.

@mmalohlava JFYI this related to https://github.com/h2oai/h2o-3/issues/15683 which you were involved in.