Add an optionnal cover for articles

[OxNinja]

Add the possibility to use a cover for posts such as:

Cover which will be displayed in the post itself, code exemple to use a cover in a post:

title: My post title
cover:
  image: cover.jpg

In the upcoming days I will try to do a PR 🙏

[kevinlinxc]

Did you figure out how to do this?

[OxNinja]

I did not have the time, and unfortunately I forgot 🥲 I don't think I will be able to PR in the upcoming weeks
If someone is interested it would be cool

[jpanther]

This is now available in Congo v2.4.0. The getting started docs have more details on how this new feature works.