[Feature] Branch without `renv` included

[aridyckovsky]

Summary

Create a branch of this repository template that does not depend on renv package management.

Motivation

Two reasons motivate an R project template version without requiring a specified package manager.

1. Some simple projects, especially those that are not using large numbers of packages, may be more approachable for beginners without a package manager
2. There are some concerns around renv's stability and readiness as a tool.

Implementation

The simplest way to pull this off is to branch off main and create a new branch called no-package-manager. Then, deactivate and remove renv from the new branch.