Hadrian: provide a key-value setting for EXTRA_HADDOCK_OPTS

There doesn't seem to be any equivalent to setting EXTRA_HADDOCK_OPTS with Hadrian. This is used in NixPkgs to set --hyperlinked-source --quickjump, although these are set by default by Hadrian, so this feature might not get much mileage.

Edited Jul 25, 2022 by sheaf

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information