winbind:varlink: Implement get group record by name

winbind:varlink: Implement get group record by name

$> userdbctl -s org.samba.winbind group "AFOREST+domain users"
Enabled services: org.samba.winbind
  Group name: AFOREST+domain users
 Disposition: regular
         GID: 20513
     Service: org.samba.winbind

$> SYSTEMD_LOG_LEVEL=7 getent -sgroup:systemd group "AFOREST+domain users"
varlink: Setting state idle-client
/run/systemd/userdb/org.samba.winbind: Sending message: {"method":"io.systemd.UserDatabase.GetGroupRecord","parameters":{"groupName":"AFOREST+domain users","service":"org.samba.winbind"}}
/run/systemd/userdb/org.samba.winbind: Changing state idle-client → awaiting-reply
/run/systemd/userdb/org.samba.winbind: New incoming message: {"parameters":{"incomplete":false,"record":{"gid":20513,"groupName":"AFOREST+domain users","members":["AFOREST+administrator","AFOREST+user1","AFOREST+krbtgt"],"service":"org.samba.winbind"}}}
/run/systemd/userdb/org.samba.winbind: Changing state awaiting-reply → processing-reply
/run/systemd/userdb/org.samba.winbind: Changing state processing-reply → idle-client
varlink: Setting state idle-client
/run/systemd/userdb/org.samba.winbind: Sending message: {"method":"io.systemd.UserDatabase.GetMemberships","parameters":{"groupName":"AFOREST+domain users","service":"org.samba.winbind"},"more":true}
/run/systemd/userdb/org.samba.winbind: Changing state idle-client → awaiting-reply-more
/run/systemd/userdb/org.samba.winbind: New incoming message: {"error":"io.systemd.UserDatabase.NoRecordFound"}
/run/systemd/userdb/org.samba.winbind: Changing state awaiting-reply-more → processing-reply
Got lookup error: io.systemd.UserDatabase.NoRecordFound
/run/systemd/userdb/org.samba.winbind: Changing state processing-reply → idle-client
AFOREST+domain users:x:20513:AFOREST+administrator,AFOREST+user1,AFOREST+krbtgt

Signed-off-by: Samuel Cabrero <scabrero@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>