Add webpack config for building prod

[jtpio]

Follow the JupyterLab config: https://github.com/jupyterlab/jupyterlab/blob/main/dev_mode/webpack.prod.config.js

To check:

• Add hash to webpack requests to enable caching jupyterlab/jupyterlab#9776

Fixes #7373
Fixes #7221

[github-actions]

👈 Launch a Binder on branch jtpio/notebook/webpack-prod

[jtpio]

This may also be related to the following issues:

• Blank page in Brave #6080
• Jupyter notebook blank page on start up #5963

[jtpio]

Postponing to 7.3.0, as this likely involves using the html-webpack-plugin to properly inject the script tag with the cache busting hash string. We might also want to take the opportunity to restructure the build so each page has its own app and bundle, similar to the approach taken in JupyterLite:

• https://github.com/jupyterlite/jupyterlite/tree/main/app/tree
• https://github.com/jupyterlite/jupyterlite/tree/main/app/consoles
• https://github.com/jupyterlite/jupyterlite/tree/main/app/notebooks

Instead of the current approach which currently builds a single bundle, and activate a specific list of plugins on each page.

[jtpio]

Closing in favor of #7513