Added filtering option for entities listing

[VukW]

Solution for https://github.com/mlcommons/medperf/issues/496 : add --valid flag for entity listing:

medperf mlcube ls --valid
medperf dataset ls --valid
medperf benchmark ls --valid
medperf result ls --valid

Waits for https://github.com/mlcommons/medperf/issues/509 to implement is_valid flag for Result entity

[github-actions[bot]]

MLCommons CLA bot All contributors have signed the MLCommons CLA ✍️ ✅