According to this issue, forcing the container to handling https “is out of scope” SSL for Docker Zammad · Issue #91 · zammad/zammad-docker-compose · GitHub .
Most users, as far as I can tell, actually use another webserver / proxy to proxy to the Zammad application within docker context. But I might be absolutely wrong here! 
(e.g. see: NGINX Reverse Proxy for HTTPS )
I thought that you might be able to use volumes to “overwrite” the configuration files - however, after a quick search I failed to find anything to that. So please take the last part of my answer as a possible way that I can’t proove and thus my mind possibly playing tricks on me. 