[Docs] Add EuiCard display prop example

[cchaos]

We might need to add an option in EUI to render EuiCard without the panel (border & shadow) display.

Originally posted by @cchaos in elastic/kibana#67467

This also occurs on the Kibana homepage with overriding styles, but would be good to have a consistent approach supplied by EUI. Though if the cards are clickable, they should still have the shadow appearance on hover/focus.

[snide]

Reminder for whoever picks this up that this one might touch amsterdam files.

[cauemarcondes]

@cchaos elastic/kibana#67467 (comment)

But it'd be very good a padding property.

[cchaos]

^^ @andreadelrio, I forgot we actually have this option already with display. (Doh!) We may still want to add a docs example for it though and look into the padding request.