dirmngr: Support the new WKD draft with the openpgpkey subdomain.
* dirmngr/server.c (proc_wkd_get): Implement new openpgpkey subdomain method.
(cherry picked from commit 914fa3be22bf8848a97a7dd405a040d6ef31e2fd)
- Signed-off-by: Werner Koch <wk@gnupg.org>