Add visuals and improved guidance for Banner when used within a Card

[sam-b-rose]

There is a bit of confusion with how using a Banner within a Card changes the appearance. We have some info on this, but it is mixed with other component guidance. Having images or rendered examples inline with the guidance would be a helpful way to highlight how the design changes based on context.

Suggestion:

• Add inline images showcasing the different banner styles based on context
• Make this information more prominent by separating it out of the bulleted list into its own section

Related issue: #1303 — comment