[Fairground 🎡] Card gap sizing

[abeddow91]

What does this change?

Abstracts card gap sizing so that we have a defined set of gap sizes that map to source space sizing.

The consumer then decides which gap size to choose, depending on the properties of the card.

The only visual change is for cards within a flexible/special container that have horizontal imaging.

Why?

Make gap sizing decision making easier to reason about and easier to extend.