Notebooks don't work with Python 3.10 (and pin too many packages)

[uri-granta]

Describe the bug
The notebooks don't currently work with Python 3.10 for a number of reasons:

1. we currently pin sphinx to 3.5.4 to work around Plotly cannot be loaded if Mathjax v3 is already loaded plotly/plotly.js#4563, but that version breaks with Python 3.10
2. we currently pin pandas to <1.0.0, which similarly breaks with Python 3.10: see Pandas error in documentation notebook #703
3. we depend on box2d, which doesn't provide wheels for Python 3.10 or a source package: see https://stackoverflow.com/questions/70323852/error-trying-to-install-python-package-box2d

We also pin some additional packages:

1. gym<0.22 (why?)
2. setuptools==65.6.3 (due to [Bug Report] Version 0.21 could not be installed. openai/gym#3176)
3. wheel==0.38.4 (due to due to [Bug Report] Building wheel for gym (setup.py) ... error openai/gym#3202)
4. Jinja2<3.1 (why?)

Expected behaviour
Support running and building notebooks with Python 3.10 and, ideally, the latest versions of all the dependant packages.

[uri-granta]

Fixed in #738