The bug was mentioned on meta: https://meta.discourse.org/t/pressing-dismiss-new-doesnt-clear-new-topics/179858
Problem is that sometimes the user has TopicUser records with `last_read_post_number` set as NULL. In that case, the topic is still "new" to them and should be dismissed when they click dismiss button.
In addition, I added that condition to post_migration and bumped the number to fix existing records. Migration is written to be idempotent so it will make no harm to already deployed instances.
Original PR was reverted because of broken migration https://github.com/discourse/discourse/pull/12058
I fixed it by adding this line
```
AND topics.id IN(SELECT id FROM topics ORDER BY created_at DESC LIMIT :max_new_topics)
```
This time it is left joining a limited amount of topics. I tested it on few databases and it worked quite smooth
Follow up https://github.com/discourse/discourse/pull/11968
Dismiss all new topics using the same DismissTopicService. In addition, MessageBus receives exact topic ids which should be marked as `seen`.
* FEATURE: Ability to dismiss new topics in a specific tag
Follow up of https://github.com/discourse/discourse/pull/11927
Using the same mechanism to disable new topics in a tag.
* FIX: respect when category and tag is selected
This is a try to simplify logic around dismiss new topics to have one solution to work in all places - dismiss all-new, dismiss new in a specific category or even in a specific tag.
