Feature request: plugins

[joelb123]

First, thanks for this project, which I find incredibly useful. This request is about avoiding duplication of work in the face of continuous integration by multiple developers. It's related to nox updates #254 about how to update the instance, but also to retrocookie and the new code under development mentioned in the roadmap #450.

Like many developers, I frequently need some components that are in common across many of my projects. Examples include institutional branding in the docs, choosing Typer rather than click, and managing complex test data downloads. Initially I took the approach that many others have of forking this project and making my own changes, but I eventually found that maintenance is nearly unsustainable due to the (commendable) speed of development of this project. I'd like to be able to create a set of independent plugins that play well with cookiecutter-hypermodern-python that allow for prepending, appending, and overloading templates at the file and functional module levels.

I envision a tool that takes a set of plugin repositories in priority order and creates a new per-project customized cookiecutter repo with the plugin repos as git subtrees. A dependency checker periodically checks those subtrees for updates and generates new commits. The instance does updates as with cruft before running the usual dependabot checks. Changes made to the instance get back-propagated with retrocookie.

I have some ideas about how to implement this, but I'm curious to get a reaction first.