refactor(feed): add TODO for configurable decorator insertion index

- Add a TODO comment to implement configurable decorator insertion index via remote config
- This change highlights the need for future improvement in feed customization

Author: fulleni

lib/shared/services/feed_decorator_service.dart

@@ -70,6 +70,7 @@ class FeedDecoratorService {
   // The zero-based index in the feed where the decorator will be inserted.
   // A value of 3 places it after the third headline, which is a common
   // position for in-feed promotional content.
+  // TODO(fulleni): Make this configurable throu the remote config.
   static const _decoratorInsertionIndex = 3;
 
   // Defines the static priority for each feed decorator. A lower number is a