Spike creating test fixtures for a single component

[36degrees]

Part of #1830

---

What

Spike creating test fixtures for a single component:

• Update the tests for that component to use the examples in the YAML file consistently
• Explore how we can create fixtures from the component YAML as part of the 'build:package' task
• Explore different formats for the fixtures – (e.g. separate files, separate folders, one file)
• Create fixtures for the single component
• Understand how including fixtures will affect the package size

Why

Doing this will:

• allow us to publish a pre-release that we can share with the community in order to get feedback
• help us uncover any unforeseen issues, or unanswered questions
• help us to better understand the complexity of implementing this for all components

[vanitabarrett]

Pre-release generated here: https://github.com/alphagov/govuk-frontend/tree/pre-release-spike-test-fixtures