Exactly as @tjb_altf4 wrote above...
If you want to have files in a directory that is mapped to a directory on the host, you have to do a initial copy script that is not located in the Dockerfile because if you do a mapping of a directory from the host to a container like you do in this instance for the /config directory the files from the container in this directory will be overridden by the directory from the host.
So to speak if the directory on the host is empty it will be also empty in the container, you can try this by removing the mapping from your template and you will have files in the /config directory (inside the container) but the changes are not persistent between container updates because the files in the /config directory are now only just a simple Docker layer that will be overwritten by a container update/rebuild.
Also as @tjb_altf4 said, don't forget to change permissions on them and also don't forget to put a check in your copy script that checks if the files are already exist in the /config directory to not overwrite the files when they already exist.