Settings toggle for html frontend needed

[hmpf]

While we are developing the html frontend we have been using the OVERRIDING_APPS/EXTRA_APPS functionality to test the new functionality, but that will be too complex for a production deployment. We'd rather have a single setting that turns the html frontend on and off. This issue is to help us keep track of what needs doing.

[hmpf]

EXTRA_APPS is currently:

[
  {
    "app_name": "django_htmx",
    "middleware": {
      "django_htmx.middleware.HtmxMiddleware": "end"
    }
  },
  {
    "app_name": "argus_htmx",
    "urls": {
      "path": "",
      "urlpatterns_module": "argus_htmx.urls"
    },
    "context_processors": [
      "argus_htmx.context_processors.theme_via_session"
    ],
    "middleware": {
      "argus_htmx.middleware.LoginRequiredMiddleware": "end"
    }
  },
  {
    "app_name": "debug_toolbar",
    "urls": {
      "path": "__debug__/",
      "urlpatterns_module": "debug_toolbar.urls"
    }
  },
  {
    "app_name": "template_partials"
  }
]

OVRRIDING_APPS is not used. Supporting debug_toolbar is not part of this issue.

[hmpf]

Settings needed so far are:

LOGIN_URL = "/accounts/login"
LOGIN_REDIRECT_URL = "/incidents/"
PUBLIC_URLS = [
    "/accounts/login/",
    "/api/",
]

This differs from the react frontend which needs:

LOGIN_URL = "/login/"
LOGIN_REDIRECT_URL = "/"

(It will probably also be necessary to adapt how we do OAuth2 as we are still testing with local logins only.)

We might no longer need the magic in "argus.dataporten.social.DataportenFeideOAuth2" in AUTHENTICATION_BACKENDS.

[hmpf]

Another question is whether we should still support the old frontend. I would prefer that we did not.