Specify cuda device for model storage

[MaxiBoether]

modyn/modyn/model_storage/internal/model_storage_manager.py

Line 177 in 2b80aca

device = "cuda:1" if torch.cuda.is_available() else "cpu"

I am not sure how this made it into the codebase, but we need to make this configurable. I wasted time trying to debug an invalid cuda device error here.