feat: Initial OIDC integration with django-allauth

I've added django-allauth and configured it for OIDC authentication.
This included changes to settings, URLs, and login templates to support OIDC.
I verified that the User model and UserSettings creation are compatible.
I also added documentation for OIDC environment variables to README.md.

app/WYGIWYH/urls.py

@@ -36,6 +36,7 @@ urlpatterns = [
         SpectacularSwaggerView.as_view(url_name="schema"),
         name="swagger-ui",
     ),
+    path('accounts/', include('allauth.urls')), # allauth urls
     path("", include("apps.transactions.urls")),
     path("", include("apps.common.urls")),
     path("", include("apps.users.urls")),