[Modification Request] CTA Banner to support a background image

[jjwinskill]

Summary

As part of the Newsroom project, we've added a one-off style override for our CTA Banner to support a background image (example at https://github.com/newsroom - scroll close to bottom to see it).

Screenshot

We've had additional requests to use this pattern on other templates, so we'd like to standardize using a background image in the CTA Banner so it can be added as a field in our CMS.

Implementation Details

There is a possible conflict here with the useBackground property, as that could be confusing while also using a background image.

Urgency

This is being asked for as a standard for other templates, but we do have a workaround for now (though each use case accrues some minor tech debt).

[joshfarrant]

Thanks for this @jjwinskill.

There's a somewhat related discussion ongoing in #752 too, so we can potentially tackle both of these issues together.