chore(react): update storybook to use fast-sass-loader in dev

[joshblack]

Update our sass config to use fast-sass-loader in development, while still using sass-loader in production builds. Also enables external CSS by default in prod.

Changelog

New

Changed

• Add copyright banners
• Update entrypoint to hooks
• Update sass strategy to use conditionally use fast-sass-loader

Removed

Testing / Reviewing

• Pull down PR
• Run yarn storybook in packages/react
• Change a style in a component file, like _button.scss and verify compilation takes <5s
• Run yarn build-storybook to build storybook files
• Run npx serve storybook-static and visit and verify project built correctly

[joshblack]

@emyarod this should address your comments from earlier!

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[emyarod]

running yarn install will also create the offline mirror for the async package which doesn't seem to be checked in? otherwise looks good to me

[joshblack]

Thanks @emyarod! Updated

[abbeyhrt]

LGTM!