[New docs] Create StoryEmbed component

[tkajtoch]

Summary

StoryEmbed component is a helper component that renders <iframe>d Storybook stories and docs views based on a given id or path.

Acceptance Criteria

• StoryEmbed should render an <iframe> element with auto-generated src
  • The src value should be generated using the STORYBOOK_ROOT_URL environment variable, the type prop, and the id or path props
• it should allow width and height customization and default to width="100%" when no value is provided

[JasonStoltz]

@tkajtoch What is the status of this?

[tkajtoch]

We decided to not embed stories as interactive examples and instead implemented an interactive example component based on react-live.