Modify model directory documentation UI and related pages

[jessica-mitchell]

This PR modifies the model directory page and how it functions as well as related pages with significant changes. There is now a interactive UI that dynamically loads results of button selection using Javascript.

See Read the Docs output here: https://nest-simulator--3203.org.readthedocs.build/en/3203/models/index.html

The script that extracted the model user docs and built the indices is heavily modified, and renamed to model_tag_setup.py, The script extracts the text and creates rst model pages and extracts the tags for each model and creates dictionaries, {model: [tags]} and [{tag: "tag", models: ["models"], count: # of models}]. These dictionaries are used in Jinja templates as well as a JSON file is created to be used by Javascript that will render the output client-side.

The models/index page now has a 'model selector' that displays each tag, in order of number of models that have that tag (with exception of neuron, synapse and device being the first tags) as multi-select buttons.
By clicking on one or more buttons the corresponding models will be displayed.

In addition to the model selector there is also a dropdown that lists in alphabetical order (grouped by neuron, synapse, and device) all models.

Some information from 'models-main' is moved into here. The page also has links to pages for more info on neurons, synapses and devices - these pages will require more work in the future but each of those pages also lists all corresponding models.

When working on this, I found that the pre-commit hook for clang would fail, so changes to it were also done, and fixes #3182
Fixes #2563

[clinssen]

The models in the list displayed by the model selector have the pilcrow character ("¶") at the end of the link; can this be eliminated?

[jessica-mitchell]

The models in the list displayed by the model selector have the pilcrow character ("¶") at the end of the link; can this be eliminated?

Yes, fixed

[clinssen]

Cheers!

[terhorstd]

Thanks for the cool new look&feel of these pages and the huge amount of work that went into this restructuring! 🚀
I think this will be highly appreciated by all users 👍

The odd thing of checking the file headers can be solved in a separate PR.