Adding r pkgs github infrastructure (QoL)

[gvegayon]

This PR adds the following:

• New GHA for automatic R CMD check: This will trigger R CMD check in multiple versions of R x hardware architectures.
• New GHA for code coverage: This generates a report using codecov.io. Notice it will fail at first, since you need to set up your account.
• New GHA for GitHub Copilot environment: GitHub Copilot takes a great deal of time setting up the environment for coding and reviewing. This GHA streamlines the process so it is more efficient.
• Patched pkgdown GHA to include an automatic posting of a comment with a preview of the pkgdown website in PRs.
• A devcontainer: Devcontainers are a great way of standardizing the development environment. This allows collaborators to set things up almost on the fly.
• Badges in the README file: Automatic badges that indicate the status of a couple of GHA workflows.