Only return one partOf for articles #237
Description
What:
Currently returns and exposes the array of partOf
Only one should be visible, as is the case on the article page at the moment:
As we'll never want more than one to display on the article card, the change should be done at the API level (not on the FE). Might be worth keeping it in the /articles/:id endpoint though, but we'll probably have to develop it further anyway when we get to using it.