Have one build per page, and use `disabledExtensions` to filter plugins

[jtpio]

We should consider restructuring 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.

Originally posted by @jtpio in #7354 (comment)

[jtpio]

#7513 already seems to be helping with the most common caching issues. So we could postpone that issue to the next 7.4.0 milestone.