Support database password files in temporal-server docker image

It would be nice to support database password files instead of plaintext database passwords in docker-compose config of the temporal-server image, allowing easy use of docker-compose secrets. Something similar to keycloak: https://github.com/keycloak/keycloak-containers/commit/d433814c1969682a6bd032604bf821c23b380200

This is a great idea.

Personally, I’d much rather see env var support first, it’s much more common.