Add Rstudio interface to Codespace dev container

[bschilder]

Should be possible with VSCode:

• https://github.com/REditorSupport/vscode-R/wiki/RStudio-addin-support
• https://github.com/revodavid/devcontainers-rstudio

or Rstudio directly:

• https://github.com/jakubnowicki/r-codespaces