Flag to upload to auto-build and upload docs as well

[gbaz]

Suggested by chris martin in this thread: https://discourse.haskell.org/t/on-onboarding-hackage-missing-documentation/4684/4

dir=$(mktemp -d dist-docs.XXXXXX)
cabal configure --builddir="$dir"
cabal haddock --builddir="$dir" --haddock-for-hackage --haddock-option=--hyperlinked-source
cabal upload --publish -d $dir/*-docs.tar.gz

Generally an all in one workflow to sdist, haddock, and upload both would be very nice and probably improve the docs situation on hackage.

Related discussions: #5064 #7566 and #3837

The latter is arguably the most comprehensive and may subsume this.

[ulysses4ever]

Related discussion in #5821

[ulysses4ever]

Probably related works as standalone tools:

• https://hackage.haskell.org/package/hackage-cli
• https://hackage.haskell.org/package/hkgr