Feature: on book's card in /books, display a picture

**Community discussion about this feature (mandatory)**
https://forum.camptocamp.org/t/suggestions-diverse-pour-le-site/284407

**Is your feature request related to a problem? Please describe.**
Books often has one image: the book cover. It would be fancy to see it on cards, as it'd help a lot to visualy identify a book.

**Describe the solution you'd like**
On books' card, display the book cover. If there is more than one picture, dio not display anything (waiting for `main picture id` feature on API).

**Describe alternatives you've considered**
na

**Additional context**
na