CI improvements

[iolivia]

We have a CI thanks to @wbprice! 🎉

Some future improvements:

• [ ] use some clever caching to share state between the different folders
• [x] automate the CI yml file to discover added/removed sample folders
• [ ] add mdbook build and test step - see https://rust-lang.github.io/mdBook/continuous-integration.html
• [ ] use clippy in the pipeline
• [ ] use prettier for the markdown files