chore(storybook): upgrade to storybook v9

[nickofthyme]

Summary

Upgrades our storybook to latest v9.

⚠️ Currently, a WIP

To test, pull down branch then run...

yarn start
cd ./.storybook
yarn && yarn start

Zight.Recording.2025-08-25.at.09.14.52.AM.mp4

Details

• Build out new storybook configuration
  • Upgrade all config files to latest config style
  • Migrate from webpack to vite
    • Fix export issues
    • Fix eui dynamic icon issues
    • Fix other miscellaneous typescript issues to work with ./src files
    • Fix import sass issues
• Handle custom addon usages
  • Upgrade storybook-addon-toggles addon to latest v9
  • Remove storybook-addon-theme-toggle
    • Now possible to use the built-in backgrounds feature.
  • Remove storybook-addon-background-toggle
    • Now possible to use @storybook/addon-themes.
• Migrate off of @storybook/addon-knobs
• Migrate all stories to use latest CSF config with Meta
  • Update ChartsStory to work with Meta type.
• Validate changes work with e2e_server and e2e tests.
  • Migrate any changed query params in testing urls.
• Fix any failing eui usages. Such as EuiMarkdown.
• Check changes in ci.

Issues

#2667

Checklist

• The proper feature labels have been added (e.g. :interactions, :axis)
• All related issues have been linked (i.e. closes #123, fixes #123)
• Unit tests have been added or updated to match the most common scenarios
• The proper documentation and/or storybook story has been added or updated
• The code has been checked for cross-browser compatibility (Chrome, Firefox, Safari, Edge)
• Visual changes have been tested with light and dark themes