Use whitenoise for static file handling (#6662)

* Update config_template.yaml file

* Adjust ALLOWED_HOSTS behaviour

- Only add wildcard * in DEBUG mode
- Exit if ALLOWED_HOSTS not defined

* Tweak error message

* Use whitenoise for serving static files

- Any requests to /static/ are handled by whitenoise
- If an external reverse proxy (e.g. Caddy) is being used, this will not make a difference

* Update python package requirements

* Add extra log output

* Update ENV for CI checks

* Updates

- Thow error but do not exit
- Revert CI changes

requirements.txt

@@ -342,6 +342,7 @@ webencodings==0.5.1
     #   cssselect2
     #   html5lib
     #   tinycss2
+whitenoise==6.6.0
 wrapt==1.16.0
     # via
     #   deprecated