debusine provide-signature --help mismatch

User story

$ debusine provide-signature --help
usage: debusine provide-signature [-h] work_request_id [extra_args ...]
[...]
  extra_args       Additional arguments passed to debsign

$ debusine --server freexian provide-signature 13913 -k 3CCCC613C34F3D54718A983CEE887356CD2F16A0
usage: debusine [-h] [--server SERVER] [--scope SCOPE] [--config-file CONFIG_FILE] [-s] [-d]
                {list-work-requests,show-work-request,...}
                ...
debusine: error: unrecognized arguments: -k 3CCCC613C34F3D54718A983CEE887356CD2F16A0

$ debusine --server freexian provide-signature 13913 -- -k 3CCCC613C34F3D54718A983CEE887356CD2F16A0
Artifact file downloaded: /tmp/debusine-debsign-ur09wgzd/aaapp_1.0-1+deb9u1_all.buildinfo
...

So the help should be:

usage: debusine provide-signature [-h] work_request_id [-- extra_args ...]

(or additional arguments should directly be passed without the need for --)

0.11.1~bpo12+1