`add-theme` script for design-tokens

[mimarz]

Requested feature from Slack for an option to use our cli @digdir/designsystemet to add scaffold new themes to design-tokens with our predefined json structure.

One obvious parameter would be theme name and colors, which again would need interop with private Token Studio files 🤔

For example npx @digdir/designsystemet add-theme Altinn --colors "#0062BA, #1E2B3C, ##F45F63, #E5AA20, #1E98F5"