dirmngr: Support the new WKD draft with the openpgpkey subdomain.

dirmngr: Support the new WKD draft with the openpgpkey subdomain.

* dirmngr/server.c (proc_wkd_get): Implement new openpgpkey subdomain
method.

--
Also includes actual backport fix from
2c6d94702a676de9fadaaf003b9c80dc76c02f92

GnuPG-bug-id: 4590
Signed-off-by: Werner Koch <wk@gnupg.org>
(cherry picked from commit 914fa3be22bf8848a97a7dd405a040d6ef31e2fd)
(cherry picked from commit 458973f502b9a43ecf29e804a2c0c86e78f5927a)

Gbp-Pq: Topic from-2.2.17
Gbp-Pq: Name dirmngr-Support-the-new-WKD-draft-with-the-openpgpkey-sub.patch