feat: allow oauth configuration per site and backend (#32656)

Allows admins to configure same oauth backend for multiple sites.

This change includes site_id in KEY_FIELDS for oauth configuration
provider allowing a backend configuration for each site.

common/djangoapps/third_party_auth/views.py

@@ -47,7 +47,7 @@ def inactive_user_view(request):
     if third_party_auth.is_enabled() and pipeline.running(request):
         running_pipeline = pipeline.get(request)
         third_party_provider = provider.Registry.get_from_pipeline(running_pipeline)
-        if third_party_provider.skip_email_verification and not activated:
+        if third_party_provider and third_party_provider.skip_email_verification and not activated:
             user.is_active = True
             user.save()
             activated = True