docker: hassle-free DB bootstrap

While it is recommended to use `POSTGRES_PASSWORD`, I think it's good when we
can bring MSF up with minimum effort from scratch.

It shouldn't be an issue from the security point of view having the DB running
in a docker container with the 5432/tcp port available only to the MSF.

docker-compose.yml

@@ -15,6 +15,8 @@ services:
     image: postgres:10-alpine
     volumes:
       - pg_data:/var/lib/postgresql/data
+    environment:
+      POSTGRES_HOST_AUTH_METHOD: trust
 
 volumes:
   pg_data: