Format all `.cabal` files in the repo with a cabal formatter

As noticed in https://github.com/haskell/haskell-language-server/pull/4224#discussion_r1597873736, non-standard formatting can make it harder to read and .cabal file.

We have now at least two good options for formatting .cabal files that we both support in HLS itself:

* cabal-gild
* cabal-fmt

Perhaps we should start using these formatters in HLS and add new CI jobs that make sure all our .cabal files are formatted accordingly.

If the output of the formatter looks unwieldy to us, we should reach out to the projects and discuss improvements.