Refactor Metric API

[vitusbenson]

Currently each setting ("dataset") comes with its own Metric. This uses the PyTorch Lightning Metric API (https://torchmetrics.readthedocs.io/en/stable/). It might be, that this API is outdated, and it might also be that Metrics are consistent across datasets, hence leading to duplicity.

Goal:

• A better API for metrics, that is added to the Task part, like the losses.
• Independence from datasets

Culprits:

• Keep using torchmetrics (https://torchmetrics.readthedocs.io/en/stable/)?