feat: FIT-14: LabelStudio Playground 2.0

[bmartel]

This pull request introduces the foundational setup and implementation of the LabelStudio Playground, a standalone React application for editing and previewing LabelStudio XML labeling configurations. This implementation will serve as the replacement of the defunct playground used on labelstud.io.

Project Setup and Configuration

• Added a .babelrc file to configure Babel with the @nx/react/babel preset for automatic runtime.
• Introduced a jest.config.ts file for unit testing, with support for Babel transformations and module name mapping.
• Added a project.json file to define build, serve, and test targets using Nx executors for Webpack and Jest.

Documentation and Overview

• Created a comprehensive README.mdc file detailing the purpose of the Playground app, its features, architecture, state management, and extensibility.

State Management

• Defined Jotai atoms in configAtoms.ts to manage application state, including configuration, loading, error, and annotation data.

UI Components

• Added a BottomPanel component to display sample data input and annotation output, with collapsible and resizable functionality. [1] [2]
• Implemented an EditorPanel component for XML editing with a resizable bottom panel for input/output display. [1] [2]

Styling

• Added SCSS styles in PlaygroundApp.module.scss to lightly customize the appearance of CodeMirror and LabelStudio components.