Allow use of secrets when using docker-compose to set password

[xivk]

In the postgres docker containers there is the option to use the following to set something sensitive like passwords:

POSTGRES_PASSWORD_FILE: /run/secrets/db-password-file

This reads the password from a text-file, a 'secret'. See also https://www.docker.com/blog/how-to-use-the-postgres-docker-official-image/

The password never leaves the server this way and doesn't end up in a git repo somewhere as opposed to using this:

DB_PASSWORD: dbpassword

Is there a way to this using this container? Are you open here to a pull request adding this feature? Or am I missing some other way to configure the password?