Background

We should strive to provide configurable demos of all our components (even the ones used 'internally'), so users can quickly understand the purpose of their props and evaluate suitability.
Including configurable sections will also allow us, in some cases, to reduce the number of instances that we need to showcase in the demo pages, since said instances can be obtained/showcased via configuration.

Goals

Following the principle stated above, we should include a configurable version of the Thumbnail component that allows users to see which of its properties can be adjusted. Technical feasibility should be confirmed but, ideally, users should be able to:

• Switch between image and placeholder thumbnails
• Edit the custom placeholder icon (applied to placeholder thumbnail only)

Acceptance criteria

• The Thumbnail demo page includes a 'Configurable' section that allows users to adjust and test the properties of this component.