initialize {renv} following sandpaper functions

[avallecam]

Thanks to @pratikunterwegs report, I found that to update the renv.lock file, one way is to reuse {sandpaper} functions, at least instead of the renv::init

The project template already has a renv.lock file within the renv/profiles/lesson-requirements path. Using renv::init creates a new renv.lock which I suspect is not appropriate for the repo.

Following the vignette on "building a lesson with package cache", we can follow these family of functions to initialize and update the files that the project already has:

sandpaper::use_package_cache()
sandpaper::manage_deps()
sandpaper::update_cache()

And a mix of them with the {renv} to check for status, snapshots, install, and possibly also to restore the environment.

[avallecam]

closing. clear instructions now at #75