UX: Various improvements to welcome topic CTA (#21010)

- Update welcome topic copy
- Edit the welcome topic automatically when the title or description changes
- Remove “Create your Welcome Topic” banner/CTA
- Add "edit welcome topic" user tip

lib/topic_query_params.rb

@@ -18,18 +18,6 @@ module TopicQueryParams
       :no_subcategories
     ].present?
 
-    if hide_welcome_topic?
-      options[:except_topic_ids] ||= []
-      options[:except_topic_ids] << SiteSetting.welcome_topic_id
-    end
-
     options
   end
-
-  private
-
-  def hide_welcome_topic?
-    return false if !SiteSetting.bootstrap_mode_enabled
-    Site.welcome_topic_exists_and_is_not_edited?
-  end
 end