update to be defang postgres ready

Author: raphaeltm

samples/django-postgres/compose.yaml

@@ -2,15 +2,19 @@ services:
   db:
     restart: unless-stopped
     image: postgres:16
+    x-defang-postgres: true
     environment:
       - POSTGRES_DB=django
       - POSTGRES_USER=django
       - POSTGRES_PASSWORD
     ports:
       - mode: host
         target: 5432
+        published: 5432
 
   django:
+    # uncomment to add your own domain
+    # domainname: example.com
     restart: unless-stopped
     build: ./app
     ports: