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

[cemms1]

Un-assigning myself and moving this to the backlog of WebX board after discussion at standup that this may not be relevant for this stage in the project.

This has been deprioritised because for DCR in apps, we are initially concentrating on achieving parity with web. Since the onwards journey component at the bottom of articles for web does not recognise if the user has seen articles before, we do not need to prioritise this work in order to launch DCR in apps.

In web, there is a recognition of whether a user has viewed an article in the onwards content on the side of an article, however. So we know we will need to revisit this, and may want to include this logic in the onwards content at the bottom of articles too. For MVP however, it's not strictly necessary.

This PR was a work in progress implementation for this ticket, but was missing the handling of both web and apps in the final Carousel component.

[rhiannareechaye]

I think we could do this 'post-prod' release - would be nice to try and get it working on the web - agreed in standup that we'll pick this up after we've gone to prod

[sophie-macmillan]

Putting this back into the backlog as I picked it up as a quick fix when on rota
WIP branch here: https://github.com/guardian/dotcom-rendering/compare/sm/dcar-filterSeenArticles