Show forum thread title in bell notification

Description

When someone responds in the forum, a bell notification is triggered. This notification has only the name of the forum - the additional info what thread the post is from would be helpful when you get swamped with messages.

Impact

Every FS (with quiz & forum access)

Proposal

Fetch & add the thread title in the Notification Bell. (Maybe optional, togglable in the settings?)

Links / references

Setting a due date for in 2 weeks. Could be moved to #795 (closed) after that date.