Backporting fixes:
- Allow PyTorch 2.0 #2724 by @lostella
- Improve check for validation loop in lightning modules #2726 by @lostella
- Update CP-Flow fork as extra dependency for MQF2 #2727 by @lostella
- Allow PyTorch Lightning 2.0 #2728 by @lostella
- Fix _version location for sdist. #2729 by @jaheba
- Add warning for "object" features in PandasDataset #2731 by @lostella
- Docs: Add extra requirements. #2732 by @jaheba
- Fix validation loop check for Lightning modules #2733 by @lostella