Blocked by T330934
Original requirement: Unlike article-level notifications, for section-level if there are images for new sections in the article that becomes available then send the notification again for the same article.
ATM we only ever send a user one image-suggestion-notification for any article. We need to change this so that we only send a user one image-suggestion-notification for any //section//
Imagine that in the past that for `Article_X` we had suggested images for the article itself, for `Section A` and for `Section B` and we send a notification about those to `User 1`
* atm if a suggestion for `Article_X#Section C` appears in the pipeline we don't send it to `User 1`, because that user has already gotten suggestions for that article
* we want to change that to allow sending the suggestion for `Section C`. Note that we do *not* want to send article-level suggestions or suggestion for `Section A` or `Section B`