[Project - Onboarding]: Set up a new React application in @storybook/addon-onboarding

[valentinpalkovic]

Description

The @storybook/addon-onboarding addon will not use the classical APIs to register tabs or panels into the manager. Instead, it should initialize a separate React application in its manager.ts entry point. Within this React application, we can implement all the necessary logic for the onboarding flow (custom modals, tooltips,...). This addon will not interact API-wise with the manager at all. The addon will only use overlays to display content. Therefore it will be distinct from the manager's layout.

Acceptance criteria:

• Mount a React application in the addon's manager.ts into the DOM. Create an empty div container at the HTML body's root element for this. Ensure the div container doesn't change/influence the manager's layout (position: absolute,...)
• Mount a dummy "Hello World" component into this new root element.