In the templates database folder in your appdata you need to create the folder "extensions" and then place the .jar for the metadata scraper available here: https://github.com/comixed/comixed-metadata-comicvine and then restart the docker.
The default property name for the api-key of the metadata scraper is also wrong, it needs to be comic-vine.api-key , not just api-key.
This worked for me just now