Set up Storybook

[cee-chen]

Summary

See: #6583

This PR installs and sets up Storybook via npx storybook@latest --type react, adds a very basic component test, and adds some extra global types in the Preview setup that lets us change our theme provider color mode and writing mode.

This is still a very basic spike and still needs a decent amount of work done around extracting props to Storybook, but since it's not being published anywhere and just lives locally, there's no harm in merging it into production and continuing to tweak as we go (e.g. adding addons, investigating Chromatic, etc).

QA

• Regression testing - run yarn start and yarn lint and ensure everything still works as before
• Run yarn storybook and confirm that a new local window opens up with an EuiErrorBoundary example
• Click the Light mode and LTR toggles in the component toolbar and confirm they change as expected per the below screencap

References

Useful docs to familiarize yourself with:

• https://storybook.js.org/tutorials/intro-to-storybook/react/en/simple-component/
• https://storybook.js.org/docs/react/essentials/controls
• Potential uses:
  • https://storybook.js.org/docs/react/writing-docs/autodocs (not sure we'll use this much 🤔)
  • https://storybook.js.org/docs/react/writing-stories/play-function (will be extremely useful for, e.g. a11y testing, visual diffing)

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_6816/

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_6816/

[cee-chen]

Thanks Ryan!