feat: Adds a new flag for discussions LTI configuration for admin only config

Some providers need special considerations when being set up so should only be
configured by people with global staff privileges. This adds an
admin_only_config flag to such providers (only YellowDig for now).

openedx/core/djangoapps/discussions/models.py

@@ -162,7 +162,8 @@ AVAILABLE_PROVIDER_MAP = {
             contact_email='learnmore@yellowdig.com',
         )._asdict(),
         'messages': [pii_sharing_required_message('Yellowdig')],
-        'has_full_support': False
+        'has_full_support': False,
+        'admin_only_config': True,
     },
     'inscribe': {
         'features': [