Update the R definition according to the extension update

[eitsupi]

Reflects the extension and the base image updates, and makes improvements that weren't in time for the last PR #954.

1. Since the settings vsc.use_httpgd = TRUE made on Rprofile can now be done from settings.json too, delete it from the Dockerfile and move it to devcontainer.json. (Accessing VS Code settings in R REditorSupport/vscode-R#743)
2. Change the VALIANT and comments which select a R version to match other definitions as the base image now pushes minor and major version tags. (Update for automated multi-tagging and reducing the number of stack files rocker-org/rocker-versioned2#214)
3. Add a new extension rdebugger.r-debugger that enable debugging of R on VS Code and the R package vscDebugger required by rdebugger.r-debugger. (Suggested by Update the R definition #954 (comment))
4. Update the test-project to resemble other definitions.
   However, I didn't add launch.json because I thought that execution using launch.json would be done on the internal console and may confuse the user. (Add "console" option to open itegrated terminal instead of internal console ManuelHentschel/VSCode-R-Debugger#147)

cc @kmehant @renkun-ken @ManuelHentschel @ElianHugh

[Chuxel]

LGTM! Thanks for the contribution!!