Add a workflow for including aquascapes in Laika docs

[zainab-ali]

Aquascapes are included in the reference docs on the aquascape website, but the workflow for this is currently internal, and scattered across the project.

• The examples module contains code that generates aquascapes for the reference guide.
• The AquascapeDirectives are laika directives used to include this code in the reference docs. These are based on code only present in examples, such as the Example trait.

The aquascape directives should be published in a way that other users can include them.