[Docs] Add documentation for nested drag & drop containers

[MarvinKlein1508]

Pull Request

📖 Description

This PR adds a new documentation for nested drag and drop containers.

🎫 Issues

Fix #3925

👩‍💻 Reviewer Notes

The demo is using some fixed colors to showcase the different drop zones clearly to the user. It isn't supposed to look pretty but to show the user how it actually works.

✅ Checklist

General

• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

Component-specific

• I have added a new component
• I have added Unit Tests for my new component
• I have modified an existing component
• I have validated the Unit Tests for an existing component

⏭ Next Steps