GitHub Actions for R-devel

Actions and workflows to build base R and related things.

SVN builds

These workflows are used in the r-svn mirror to build and check on each commit to base R. The results are also published on the svn-dashboard.

Windows Dailies

The actions are also used by the windows-arm64 repo to publish the latest Windows installers for R-devel and R-patched every day.

We do not publish Linux dailies for now, I recommend those from: https://github.com/rstudio/r-builds