update docs and related tooling

[kMutagene]

This PR will

• [x] update toolchain to use .net 8
• [x] update to fsdocs 20+
• [x] remove all TOCs from docs as they are now generated
• [ ] refactor all docs into notebooks

Note that the docs of this repo are somehow cursed. I managed to fix the integration docs, which are currently not displaying output, but somehow broke signal processing and fit quality docs. I think the only solution for this is moving docs from scripts to notebooks, as they have their own mechanism of embedding output. This has the big advantage of writing docs in notebooks though, with markdown rendering and chart embedding. Disadvantage is that i have to copy paste a lot.

Anyways, @bvenn can you maybe try this out locally? maybe the broken docs output is a local problem?

Here is a side-by-side, left and middle are new theme dark/light, right is old theme:

[bvenn]

Looks great @kMutagene :rocket: Especially the site-index on the right is nice! Actually, I liked the dark-theme code cells even in the light theme layout, but maybe it just looks more familar and therefore I'm biased :wink: I can reproduce the FitQuality and SignalProcessing and going to have a look at it. Could you provide a minimal working example of how to migrate the docs to notebooks so I can start to copy-paste the contents?