Expose banner type as a variable

Problem/Motivation

The `type` variable for Banner is unset in https://github.com/civictheme/monorepo-drupal/blob/develop/web/themes/co...

This was initially done to hide the logic within Drupal.

However, during working on the consumer sites it appeared that this could be useful to be exposed and be made available in template so that the implementations could provide custom handling based on the type (CSS rules, display logic etc).

Proposed resolution

Expose the `type` variable.

Remaining tasks

Expose the `type` variable.

User interface changes

None

API changes

Banner will now have a new `type` variable exposed.

Data model changes

None