Set up sourcemaps for storybook

[gfellerph]

When inspecting styles in storybook, all styles originate from the same, compiled CSS file which is not really helpful for debugging.

Can we set up source mapping for storybook to see what sass file stuff is coming from?

[imagoiq]

Note sure if it's possible:

storybookjs/storybook#19464
storybookjs/storybook#9901 (comment)

[imagoiq]

I've found this issue: vitejs/vite#2830 (and this related documentation: https://vitejs.dev/config/shared-options.html#css-devsourcemap)
CSS sourcemap aren't built by default with Vite. At the moment, you can only build them in dev mode.