DEV: Use serializers for user_notification_schedule and featured_topic (#27719)

Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>

spec/serializers/current_user_serializer_spec.rb

@@ -352,4 +352,25 @@ RSpec.describe CurrentUserSerializer do
       expect(initial_count).to eq(final_count)
     end
   end
+
+  describe "#featured_topic" do
+    fab!(:featured_topic) { Fabricate(:topic) }
+
+    before { user.user_profile.update!(featured_topic_id: featured_topic.id) }
+
+    it "includes the featured topic" do
+      payload = serializer.as_json
+
+      expect(payload[:featured_topic]).to_not be_nil
+      expect(payload[:featured_topic][:id]).to eq(featured_topic.id)
+      expect(payload[:featured_topic][:title]).to eq(featured_topic.title)
+      expect(payload[:featured_topic].keys).to contain_exactly(
+        :id,
+        :title,
+        :fancy_title,
+        :slug,
+        :posts_count,
+      )
+    end
+  end
 end