Allow passing tuple of [low, high] to iou_thresholds parameter in DetectionMetrics.

[BloodAxe]

This PR allows to pass user-defined target of IoU thresholds without asking user to edit IoUThresholds enum in SG codebase:

valid_metrics_list:
  - DetectionMetrics:
      iou_thres: [0.5, 0.8]

Note that this does not solve the problem of having two instances of DetectionMetrics in valid_metrics_list, but it allow to pass iou_thres as a tuple which we do not allow at the moment

[Louis-Dupont]

LGTM