Document test-show-details (and direct for show-details)

> However, please consider test-show-details: direct (that's what I use in all my cabal.project.local files)

Is this documented in the manual? I can't seem to find either `test-show-details` or `direct` there. If that's so, it looks like a pretty major omission and worth a ticket. There's `Setup.hs test show-details` but it doesn't list `direct` as a possible value.

_Originally posted by @ulysses4ever in https://github.com/haskell/cabal/issues/8604#issuecomment-1327017555_