Upgrade to Storybook v8

[fregante]

Migration guide: https://storybook.js.org/docs/migration-guide

First dependabot attempt: https://github.com/pixiebrix/pixiebrix-extension/pull/7902

The biggest problem is that they dropped Storyshot altogether. My guess is that someone will at some point publish a fork so our migration will be easier. This is the current Storyshot migration guide: https://storybook.js.org/docs/writing-tests/storyshots-migration-guide