added 260907 version of worker toolkit

worker-toolkit-flaredown/repo/backend/app/models/topic_following.rb

@@ -0,0 +1,11 @@
+class TopicFollowing
+  include Topicable
+
+  def add_topic(key, value)
+    return if send(key).include?(value)
+
+    send(key) << value
+
+    save
+  end
+end