Some of the extension's files are not available in the notebook

Bug description

My custom Jupyter Notebook extension consist of the main.js file but also other files - JS helpers and React build artifacts. I install the package and enable the extension using the command

sudo -E jupyter nbextension install connector-jupyter --py --sys-prefix
sudo -E jupyter nbextension enable connector-jupyter --py --sys-prefix

All of the files are properly copied to the nbextensions directory:

admin@tec-l-011630:~$ ls /opt/tljh/user/share/jupyter/nbextensions/mstr_jupyter
MicroStrategy.yaml  cells-creation.js  iframe_style.css  main.js  
mstr-connector  mstr.ico  override_style.css  package-lock.json  python-code.js  utilities.js

When I run the extension in the Notebook however, only the main.js file is exposed on the server. Fetching others results in 404 error making the extension unusable.

Expected behaviour

All files are exposed on the server as it's in the case of the "desktop version" of Jupyter Notebook

Actual behaviour

Only the main.js file is exposed on the server making the extension unusable.

How to reproduce

Install mstrio-py
```
sudo -E pip install mstrio-py
```

Enable the extension

sudo -E jupyter nbextension install connector-jupyter --py --sys-prefix
sudo -E jupyter nbextension enable connector-jupyter --py --sys-prefix

Run the Notebook
Open browser's Developer Tools
Go to Sources tab
In the left panel navigate to nbextensions/mstr_jupyter directory
Observe that only main.js file is there.

Your personal set up

OS: Ubuntu 20.04 LTS

Version: How do I actually check which version of TLJH do I have?

admin@tec-l-011630:~$ sudo jupyterhub --version
sudo: jupyterhub: command not found

Configuration:

admin@tec-l-011630:~$ sudo tljh-config show
users:
admin:
- admin

jupyterhub / the-littlest-jupyterhub