chore(storybook): update to 10.x

[seanes]

https://storybook.js.org/blog/storybook-10/

Upgrade Storybook to v10.x and update related tooling.

• Bump Storybook + addons to 10.1.x
• Switch Storybook tests from @storybook/test-runner to Vitest (@storybook/addon-vitest)
• Simplify CI Storybook test setup
• Update Storybook config to SB10 APIs
• Bump Node to 22 and Vite to 7

I had to changed browser for tests to firefox for it work (cf. storybookjs/storybook#33347)
The tests are still a bit slow in CI, but blazing fast locally.

Related Issue(s)

#900

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[allinox]

Here we gooo v10! 🚀😁