Implement pip installation of jupyter lab extension

[joseberlines]

PROBLEM
When coding in a jupyter hub environement with jupyter 3.0 it's only possible to to install jupyter lab extensions for individual users if the installation it's done via pip

solution
follow the documentation for building JLab extensions for JLab 3.0. If you do it, then a pip install is sufficient, and there's no need to rebuild the image everytjme an individual user would like to install lux which is not part of the base image

See here:
https://jupyterlab.readthedocs.io/en/stable/user/extensions.html#id12

As the documentation tell us:
There are two types of JupyterLab extensions: a source extension (which requires a rebuild of JupyterLab when installed), and a prebuilt extension (which does not require a rebuild of JupyterLab). Rebuilding JupyterLab requires Node.js to be installed.

The goal here is NOT HAVING TO REBUILD JUPYTER LAB which is not possible for a jupyter hub Server based user.
A prebuilt extension could be simply installed with pip.

[owenlamont]

I hope this can be started, now jupyter lab 4 is out I'm not sure Lux will even be usable with that if the lab extension isn't installable by PyPi/Conda.