Is your feature request related to a problem?

Often I have several lessons that coverthe same files. I want these files to appear in the lesson for context to the user - so the result is that I have mutiple files with the same name and same content duplicated among multiple lessons.
Currently I copy them between each lesson - but then I change one of them and forget to update the rest and it becomes hard to maintain.

Describe the solution you'd like.

In the content.md in the front matter - allow to referene files from other lessons, and they'll be included here as well - something like:

---
type: lesson
title: Custom Filter
template: relations
focus: /frontend/Page.tsx
files:
  - ./previous-lesson/_files/shared/Order.ts
---

Describe alternatives you've considered.

Duplicating files - but that's hard to maintain

Additional context

No response