Updates DnD example to leverage iframe mode

[igor-grubic]

Description

Updates existing DnD example to leverage the iframe: true prop which enables drag and drop over different origins. Additionally added several dropzones to showcase that dnd works also while scrolling.

Related Issue

Motivation and Context

Screenshots (if appropriate)

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [ ] I have signed the Adobe Open Source CLA.
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.