2e78045a fixed the anonymization job so that it correctly updated self-mentions, which are not logged in the post_actions table. The solution was to scan the entire `posts` table with an `raw ILIKE` query. On sites with many posts, this can take a very long time.
This commit updates the job to take a two-pass approach:
First, we update posts based on the post_actions table. This is much more efficient than a full table scan, and takes care of all 'non-self' mentions.
Then, we make a second pass using the `raw ILIKE` approach. Since we already took care of most posts, we can scope this down to self-mentions only. By filtering the query to a specific posts.user_id, it is significantly more performant than a full table scan.