FEATURE: Add weekly bookmark cleanup code (#10899)

When posts or topics are deleted we don't want to immediately delete associated bookmarks, so we have a grace period to recover them and their reminders if the post or topic is un-deleted. This PR adds a task to the Weekly scheduled job to go and delete bookmarks attached to posts or topics deleted > 3 days ago.

app/models/bookmark.rb

@@ -103,6 +103,20 @@ class Bookmark < ActiveRecord::Base
       .order('date(bookmarks.created_at)')
       .count
   end
+
+  ##
+  # Deletes bookmarks that are attached to posts/topics that were deleted
+  # more than X days ago. We don't delete bookmarks instantly when a post/topic
+  # is deleted so that there is a grace period to un-delete.
+  def self.cleanup!
+    grace_time = 3.days.ago
+    DB.exec(<<~SQL, grace_time: grace_time)
+      DELETE FROM bookmarks b
+      USING topics t, posts p
+      WHERE (b.topic_id = t.id AND b.post_id = p.id)
+        AND (t.deleted_at < :grace_time OR p.deleted_at < :grace_time)
+    SQL
+  end
 end
 
 # == Schema Information