Add Fréchet inception distance as metric

[Warvito]

Add Fréchet inception distance as a new metric. It should allow to use 2D and 3D inputs. For 2D, it should have the option to chose to use a network pretrained on Imagenet (from torchvision) or a network pretrained on radimagenet (https://github.com/RichardObi/medigan/blob/18283898015cf7ac98ffc499e7f15b5ddabb57b6/tests/fid.py or https://github.com/BMEII-AI/RadImageNet). For 3D, it should use MedicalNet3D (https://github.com/Tencent/MedicalNet)

[danieltudosiu]

I would say to keep this in line with PIQ and offer feature extractors instead. This allows for better generalisability of the code and less code to maintain.