Add `reading:autoplay:gifs` to /api/v1/preferences (#22706)

app/serializers/rest/preferences_serializer.rb

@@ -7,6 +7,7 @@ class REST::PreferencesSerializer < ActiveModel::Serializer
 
   attribute :reading_default_sensitive_media, key: 'reading:expand:media'
   attribute :reading_default_sensitive_text, key: 'reading:expand:spoilers'
+  attribute :reading_autoplay_gifs, key: 'reading:autoplay:gifs'
 
   def posting_default_privacy
     object.user.setting_default_privacy
@@ -27,4 +28,8 @@ class REST::PreferencesSerializer < ActiveModel::Serializer
   def reading_default_sensitive_text
     object.user.setting_expand_spoilers
   end
+
+  def reading_autoplay_gifs
+    object.user.setting_auto_play_gif
+  end
 end