Utilize RStudio Package Manager for Docker Images

[JosiahParry]

dock_from_renv() writes a Dockerfile with cran.rstudio.com as the CRAN repository which does not serve linux binaries. For a better experience, RStudio Package Manager should be added as the default package repo to avoid building packages from source.

https://github.com/ThinkR-open/dockerfiler/blob/e40f804e9728afb9bb5a8c52d965c9ac4a8fd58a/R/dock_from_renv.R#L53