Update for R >= 4.0.0 etc.

[gorcha]

Hi!

This PR updates the underlying rocker image to R 4.1.1 and updates other software versions, with a few associated updates:

• Update JDK to 11 (8 is no longer supported in the rocker image)
• Use Ubuntu deb for PowerShell now that the image is Ubuntu based
• Update the RStudio config location (moved in recent versions)
• Updates for recent code-server

This should close #1

[pstdenis]

Line 108 of configs/shinyproxy/application.yml changes the port from 8443 to 8080, why is this? It seems to cause things to break in ShinyStudio stack

[gorcha]

Hi @pstdenis - couldn't tell you why exactly, but I would assume this is just to suit the vscode container.

This isn't one of the changes I made in this PR, it was already in the dev branch (from commit 8cd78b5).