OPL-83: Change way settings are loaded

[dborowiecki]

TICKET: OPL-83

[qgerome]

Please, do not merge that. It's too complex and I can't see what could justify to use such system instead of adding a block of text in the modules' readme explaining what are the settings that need to be added/updated in the settings.py.

You could also use another settings.mycase.py file overriding the default one with your custom configuration using the DJANGO_SETTINGS_MODULE env variable. https://docs.djangoproject.com/en/4.0/topics/settings/#designating-the-settings

IMHO, customising the settings.py is not the responsibility of the modules but the developer/implementer. (and it's a one-time operation)