🔧(backend) configure Authorization Code authentication

Integrate 'mozilla-django-oidc' dependency, to support
Authorization Code flow, which is required by Agent Connect.

Thus, we provide a secure back channel OIDC flow, and return
to the client only a session cookie.

Done:
- Replace JWT authentication by Session based authentication in DRF
- Update Django settings to make OIDC configurations easily editable
- Add 'mozilla-django-oidc' routes to our router
- Implement a custom Django Authentication class to adapt
'mozilla-django-oidc' to our needs

'mozilla-django-oidc' routes added are:
- /authenticate
- /callback (the redirect_uri called back by the Idp)
- /logout

src/backend/core/urls.py

@@ -2,6 +2,7 @@
 from django.conf import settings
 from django.urls import include, path, re_path
 
+from mozilla_django_oidc.urls import urlpatterns as oidc_urls
 from rest_framework.routers import DefaultRouter
 
 from core.api import viewsets
@@ -26,6 +27,7 @@ urlpatterns = [
         include(
             [
                 *router.urls,
+                *oidc_urls,
                 re_path(
                     r"^templates/(?P<template_id>[0-9a-z-]*)/",
                     include(template_related_router.urls),