wkd: New command --print-wkd-hash for gpg-wks-client.

wkd: New command --print-wkd-hash for gpg-wks-client.

* tools/gpg-wks-client.c (aPrintWKDHash): New.
(opts) : Add "--print-wkd-hash".
(main): Implement that command.
(proc_userid_from_stdin): New.
* tools/wks-util.c (wks_fname_from_userid): Add option HASH_ONLY.
(wks_cmd_print_wkd_hash): New.
--

GnuPG-bug-id: 4418
Signed-off-by: Werner Koch <wk@gnupg.org>
(cherry picked from commit 64621f1f40c31c7f453da98efb860ff8cf11edbc)

Gbp-Pq: Topic from-2.2.15
Gbp-Pq: Name wkd-New-command-print-wkd-hash-for-gpg-wks-client.patch