DCAR - migrate `filterSeenArticles` for user service

[cemms1]

For the related content links at the bottom of an AR article, the cards are faded (opacity changed to 0.7 for both title and image) if a user has already "seen" or visited the article that the card represents.

This uses the filterSeenArticles method on the Bridget userClient in order to find which articles have been seen or not.

Example URL: https://mobile.guardianapis.com/uk/rendered-items/society/2023/aug/29/scrapping-of-housebuilder-water-pollution-rules-to-cost-taxpayer-140m

Try adding the class fade to the cards in the "More on this story" section to see the effect