[Feature Request] Save AUC metrics as file

Feature

I would like to save evaluation metrics like the AUC from the evaluation (https://gitlab.cern.ch/gnn4itkteam/acorn/-/blob/dev/acorn/utils/eval_utils.py?ref_type=heads#L482).

Motivation

This would be helpful to further process the metric values as they are now only exposed via plots. For now, I would be interested in the AUC, but this could be extended of course.

Required Changes

Option 1: Add it to the graph_roc_curve function but I feel this is not the best place as it is mainly about plotting.

Option 2: Create a new function save_auc which could be configured in the config.yaml.