Add spacing variables to repository and add a story to display them.
Jira: https://jira.it.helsinki.fi/browse/DS-65
Figma: https://www.figma.com/design/XHPvq3wuJA9eYAbU9b9NeI/University-of-Helsinki-Design-System-%E2%80%93-2024?node-id=1704-19526&node-type=frame&t=ReqHhy3o8PvYkJSH-0