PERF: Do not include thumbnail information in default topic list payload (#10163)

Now it is only included when a theme/plugin has requested it.

app/serializers/listable_topic_serializer.rb

@@ -31,7 +31,7 @@ class ListableTopicSerializer < BasicTopicSerializer
   has_one :last_poster, serializer: BasicUserSerializer, embed: :objects
 
   def image_url
-    object.image_url
+    object.image_url(enqueue_if_missing: true)
   end
 
   def thumbnails
@@ -39,6 +39,10 @@ class ListableTopicSerializer < BasicTopicSerializer
     object.thumbnail_info(enqueue_if_missing: true, extra_sizes: extra_sizes)
   end
 
+  def include_thumbnails?
+    ThemeModifierHelper.new(request: scope.request).topic_thumbnail_sizes.present? || DiscoursePluginRegistry.topic_thumbnail_sizes.present?
+  end
+
   def include_unicode_title?
     object.title.match?(/:[\w\-+]+:/)
   end