Add support for renv

[nuest]

See https://www.robertmylesmcdonnell.com/content/posts/docker/ for a complete example and potentially good approach to enable a locked environment in a container with renv.

Also: https://rstudio.github.io/renv/articles/docker.html

[nuest]

https://twitter.com/JosiahParry/status/1422659733761269763 seems to have it all.

By @JosiahParry

[JosiahParry]

Hi @nuest I'm happy to consider putting the functionality in this package. It seems to have a bit more adoption. Do you have a similar R6 constructor? That's the key benefit of dockerfiler. It provides a very syntactically night interface for creating a dockerfile.