Improved `DatasetNotFound` error message

[klakhov]

Motivation and context

How has this been tested?

Checklist

• [ ] I submit my changes into the develop branch
• [ ] I have created a changelog fragment
• [ ] I have updated the documentation accordingly
• [ ] I have added tests to cover my changes
• [ ] I have linked related issues (see GitHub docs)
• [ ] I have increased versions of npm packages if it is necessary (cvat-canvas, cvat-core, cvat-data and cvat-ui)

License

• [ ] I submit my code changes under the same MIT License that covers the project. Feel free to contact the maintainers if that's a concern.

Summary by CodeRabbit

• New Features

  • Enhanced dataset import functionality for various formats including Cityscapes, Datumaro, KITTI, LabelMe, LFW, Market1501, VOC, MOT, MOTS, OpenImages, Pascal VOC, PointCloud, VelodynePoint, VGGFace2, WiderFace, and YOLO.

• Bug Fixes

  • Improved error message for DatasetNotFoundError to provide clearer information.

• Documentation

  • Updated to reflect new dataset import capabilities and improved error messaging.

• Refactor

  • Streamlined dataset detection and import processes for better performance and maintainability.