chore(docs): upgrade to Storybook 6

[connor-baer]

Closes #578.

Purpose

From #578:

The next major version of Storybook, our development environment & documentation tool, was released this week. Most notably, it greatly improves support for TypeScript and adds Storybook Args, a new API for interactive component examples.

We've started to gradually migrate Circuit UI to TypeScript (#516). All changes and new components should be done in TypeScript. Upgrading Storybook now would make our lives a lot easier while enabling powerful new features.

Among other things, this fixes the props table for TypeScript components.

Approach and changes

• upgrade all Storybook dependencies to v6
• fix incompatibilities, remove deprecated code, and apply migration steps as outlined in the migration guide
• rename *.story.* files to *.stories.*

Definition of done

• Development completed
• Reviewers assigned
• Unit and integration tests
• Meets minimum browser support
• Meets accessibility requirements

[vercel]

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[codecov]

Codecov Report

Merging #660 into canary will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           canary     #660   +/-   ##
=======================================
  Coverage   93.52%   93.52%           
=======================================
  Files         131      131           
  Lines        2241     2241           
  Branches      651      651           
=======================================
  Hits         2096     2096           
  Misses        119      119           
  Partials       26       26           

Impacted Files	Coverage Δ
src/components/Carousel/components/Slide/Slide.js	100.00% <100.00%> (ø)
...components/Table/components/TableCell/TableCell.js	100.00% <100.00%> (ø)

[github-actions]

🎉 This PR is included in version 2.1.0-beta.1 🎉

The release is available on:

• npm package (@beta dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[github-actions]

🎉 This PR is included in version 2.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀