Per-notebook composer autoloading?

[castarco]

It would be nice to allow install per-notebook packages using composer, with automatically enabled autoloading for those per-notebook packages.

BUT, we have to confirm in first place if that's even possible:

• [ ] Confirm the possibility of attaching some metadata to notebook files, like directory paths, to store related vendor packages.
• [ ] In case it's possible, implement this nice feature.

[castarco]

I've asked in the Jupyter Client repository issues tracker: https://github.com/jupyter/jupyter_client/issues/153