[Docker] Alpine image fix (#9118)

* Revert to alpine3:20 / postgres:16

* Remove old hack

- No longer needed as we are using python 3.11

* Update package requirements for devcontainer

Also fixes some docker warnings from the alpine Dockerfile

* Specify SITE_URL

* Reduce log output during docker image testing

docs/mkdocs.yml

@@ -285,7 +285,7 @@ extra:
   min_python_version: 3.9
   min_invoke_version: 2.0.0
   django_version: 4.2
-  docker_postgres_version: 17
+  docker_postgres_version: 16
 
   version:
     default: stable