[r-apt][r-rig] Install httpuv for VSCode

[eitsupi]

See https://github.com/REditorSupport/vscode-R/releases/tag/v2.8.0

A new experimental setting r.session.useWebServer is added to support communicating with R session via a web server running in R. This requires R package httpuv to be installed. Currently,
it enhances the session symbol completion when accessing R object via $ and @. This feature is
experimental and may be subject to change in the future. (REditorSupport/vscode-R#1151)

https://github.com/rstudio/httpuv