That is, but I can be wrong, not the intention of the docker images. They do a lot of things right and do document how to use them. Not in the official documentation but in the README.md of the project, which is located here:
Nevertheless, I’ve opened an issue and submitted a PR for adding the ability to read the DB password from a file. This way it can be used with docker secrets or other vault technologies.
In the PR are also improvements on the quality like checking the necessary environment variables and giving meaningful error messages if not met.