Add mounts for `openpose` (#387)
Upon enabling the ControlNet addon from
https://github.com/AbdBarho/stable-diffusion-webui-docker/pull/385 one
might want to use the `openpose` preprocessors. Those are downloaded by
the addon the first time they are used. Without proper mounts those
networks will be downloaded on usage after each container start.
This PR enables those mounts to reduce data traffic.