Convert tutorial markdown to jupyter notebooks and publish using nbsphinx

[cmungall]

Currently the tutorial is hard to maintain - it uses a homegrown format to run all embedded scripts and check results against what is there.

Instead we could just author the tutorial as notebooks, in the docs/ folder, enable nbsphinx which will render them (statically) as part of the docs. It's then very easy to extend the tutorial or add new examples or change examples in existing pages.

We currently do this in the linkml-transformer repo, here is an example
https://linkml.io/linkml-transformer/#examples/Tutorial/
But note this is a mkdocs repo, we use mknotebooks which may look different

Some potential downsides

1. Our tutorials focus on command line usage rather than python usage. The !s to run a script in bash may be distracting
2. The documentation may end up looking like a notebook, e.g. with numbered cells (todo: investigate if nbsphinx allows disabling this; I like how it looks in mknotebooks