[WIP] Confusion matrix and IoU

[kumuji]

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What does this PR do?

Draft that is trying to fix #1302 , #1299 , potentially #1295 , since TP, FP and FN can be extracted from confusion matrix

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[kumuji]

Oops, I saw in #1488 it is already done.

[justusschock]

yes, and also this is not a pure torch metric. If you want to implement those, make sure, to always use TensorMetric and work on pure torch tensors (specifically no numpy!) We got the numpy versions in #1327