make the externa/exposed port configurable

templates/docker-compose.yml.j2

@@ -12,6 +12,8 @@ services:
       POSTGRES_PASSWORD: {{ postgres_password }}
     volumes:
       - {{ postgres_data_folder }}:/var/lib/postgresql/data
+    ports:
+      - {{ postgres_external_port }}:5432
 
   adminer:
     image: adminer