Bump @storybook/addon-essentials from 7.0.18 to 7.0.20 in /website

Bumps [@storybook/addon-essentials](https://github.com/storybookjs/storybook/tree/HEAD/code/addons/essentials) from 7.0.18 to 7.0.20.
- [Release notes](https://github.com/storybookjs/storybook/releases)
- [Changelog](https://github.com/storybookjs/storybook/blob/v7.0.20/CHANGELOG.md)
- [Commits](https://github.com/storybookjs/storybook/commits/v7.0.20/code/addons/essentials)

---
updated-dependencies:
- dependency-name: "@storybook/addon-essentials"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>