Thebe Lite support (experimental)

The idea is to have live code execution available through JupyterLite. This feature already exists in Thebe, through the Lite package.

The only problem is that Jupyter Book only supports connecting to Binder kernels, and has no out-of-the-box solutions for Lite. Support requires extra steps beyond the usual building, which is hopefully made opaque through the use of a shell script (and later on a docker container). These steps only change the Thebe functionality, so the book can be viewed normally otherwise. Additionally, it's required that the book is hosted by a server for Lite to work.

Currently there are the following drawbacks:

• Loading the full kernel takes a long time (+30 seconds).
• It requires an extra step in the build process, which is hacky in nature.
• Thebe Lite is experimental and may have breaking changes in the future.

The advantages are:

• We don't rely on an external service (Binder), and its variability.
• We don't have to host a kernel ourselves, which is expensive.
• It doesn't introduce any security issues on the server side.