`GET /api/v2/remotes/{name}/objects` dropped the `prefix` query parameter, so a filtered listing returned the first page of every artifact in the remote.
- add a `prefix` argument to `ListArtifacts` that matches path prefixes
- pass the `prefix` query parameter through from the objects list handler
Reviewed-on: #129
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>