Switch from Cabal to Stack script once LTS resolver with `pandoc >= 3.0` is available

[jcpaik]

Right now the preprocessor is a Cabal script. I would have prefered to use a stack script like this

#!/usr/bin/env stack
{- stack script --resolver=nightly-2023-02-14 --verbosity=info
  --package process
  --package pandoc
  --package pandoc-types
  --package text
-}

but it just don't give me the needed Pandoc >= 3.0 saying that it is hidden. LTS resolvers work with no 'hidden package' error, but it doesn't have >= 3.0 and I already wasted a full working day on it just to make it work. I might better make a full project, but this is just a script and I don't want all the extra steps/files to compile and run.

[jcpaik]

Cabal seems to work fine.