✨(backend) support Agent Connect Logout flow

The default Logout view provided by Mozilla Django OIDC is not suitable
for the Agent Connect Logout flow.

Previously, when a user was logging-out, only its Django session was ended.
However, its session in the OIDC provider was still active.

Agent Connect implements a 'session/end' endpoint, that allows services to
end user session when they logout.

Agent Connect logout triggers cannot work with the default views implemented
by the dependency Mozilla Django OIDC. In their implementation, they decided
to end Django Session before redirecting to the OIDC provider.

The Django session needs to be retained during the logout process.

An OIDC state is saved to the request session, pass to Agent Connect Logout
endpoint, and verified when the backend receives the Logout callback from Agent
Connect. It seems to follow OIDC specifications.

If for any reason, the Logout flow cannot be initiated with Agent Connect,
(missing ID token in cache, unauthenticated user, etc), the user is redirected
to the final URL, without interacting with Agent Connect.

src/backend/core/authentication/urls.py

@@ -0,0 +1,18 @@
+"""Authentication URLs for the People core app."""
+
+from django.urls import path
+
+from mozilla_django_oidc.urls import urlpatterns as mozzila_oidc_urls
+
+from .views import OIDCLogoutCallbackView, OIDCLogoutView
+
+urlpatterns = [
+    # Override the default 'logout/' path from Mozilla Django OIDC with our custom view.
+    path("logout/", OIDCLogoutView.as_view(), name="oidc_logout_custom"),
+    path(
+        "logout-callback/",
+        OIDCLogoutCallbackView.as_view(),
+        name="oidc_logout_callback",
+    ),
+    *mozzila_oidc_urls,
+]