♿ [#2625] Add skip-link design tokens

[jiromaykin]

This PR was made to serve this issue: https://taiga.maykinmedia.nl/project/open-inwoner/task/2625
PR: maykinmedia/open-inwoner#1470

I based these on the current Community tokens: https://nl-design-system.github.io/utrecht/storybook/?path=/story/css_css-skip-link--design-tokens

[jiromaykin]

@pi-sigma @swrichards This may not look very exciting, but this is the simple addition of a new design-token for a new tiny component.
The naming convention of these variables depend on the 'style-dictionary' NPM package and the NLDS variables naming conventions.
If you run this locally you should see this package will create a CSS file in the 'dist' folder.
This package version was published here: https://www.npmjs.com/package/@open-inwoner/design-tokens?activeTab=versions
So when approved, this means we can start using the updated version of this CSS in this other PR later on: maykinmedia/open-inwoner#1470