Modernize documentation setup

[LaurentRDC]

This PR does two things:

• Modernize the way documentation is built by re-using the flake.nix mechanism for development;
• Generates documentation on every commit and deploy to Github Pages once again.

Fixes #612 and #727

Modernization

There were a few issues that needed to be fixed.

The most important is that I could not get the dbLenses and tableLenses mechanism so compile on GHC 9.8 or 9.10. I recall there were changes to ImpredicativeTypes in GHC 9.8, so it could be why. Instead, I generated lenses using microlens-th's makeLenses, and edited the section on lenses accordingly (i.e. practically removed it).

This introduced TemplateHaskell in some of the examples. Unfortunately, runhaskell doesn't work well with staged compilation of files containing TemplateHaskell. Therefore, we build examples with runhaskell UNLESS Template Haskell is involved, in which case we use the much slower ghc --make -O0.

[LaurentRDC]

@peterbecich I extended your implementation of flake.nix from #737 to also work with the documentation, but I'm very far out of my depth here. Would you take a look?

Edit: I'll merge the PR now since it's working, but feel free to comment here and I can make fixups in a subsequent PR