FIX: Notify tag watchers when publishing topic (#17576)

When a topic was published from a shared draft and it had tags, the
users watching the tags were not notified. The problem was that the
topics are usually created in a secret category and publishing it just
moves an existent topic to the target category, without making any
changes to the tags.

lib/topic_publisher.rb

@@ -46,6 +46,14 @@ class TopicPublisher
       end
     end
 
+    Jobs.enqueue(
+      :notify_tag_change,
+      post_id: @topic.first_post.id,
+      notified_user_ids: [@topic.first_post.user_id, @published_by.id].uniq,
+      diff_tags: @topic.tags.map(&:name),
+      force: true,
+    )
+
     MessageBus.publish("/topic/#{@topic.id}", reload_topic: true, refresh_stream: true)
 
     @topic