Update whetstone hostname to private.storage.

Note that changing the origin repository in the on-node deployment checkout is also required.

See https://whetstone.private.storage/privatestorage/privatestorageops/-/merge_requests/197#note_19071

This is the result of running

sed -i 's/whetstone.privatestorage.io/whetstone.private.storage/g' $(rg -l whetstone.privatestorage.io)

on the repository.