Implement MyST-NB to run notebooks in docs

[reint-fischer]

Implementing MyST-NB as a sphinx extension will replace both nbsphinx and myst_parser. This way, we can read and execute both .md and .ipynb notebooks, which will allow us to write new notebooks in .md for better integration with the rest of the documentation.

TODO

• add myst_nb remove myst_parser
• transfer .ipynb execution from nbspinx to myst_nb
• Execute quickstart tutorial on docs build
• Execute quickstart tutorial during CI?
• Fix User Guide links: nbgallery alternative in MyST-NB
• Finish writing quickstart tutorial as .md notebook

Fixes #2335

[reint-fischer]

I managed to build the docs using MyST-NB and I think the docs look pretty good, which I think is exciting! The main observations I have so far:

• building the docs already took a couple of minutes with only 5 notebooks, but that was only the first time. Notebooks are only executed if they have changed so once I am only working on the quickstart tutorial it is pretty much as quick as before.
• writing new notebooks is more challenging because I cannot execute the cells in VS Code as I am editing them. There might be a way to do this?
• I still need to look into the printing of outputs, such as the progressbar and with the docs in “dark mode"