Create script that takes wandb checkpoint and creates/uploads hessian spectra plot

[Diego]

Description

Port nesta's code into something readable, please.

Create a script experiments/plot_hessian.py that takes as inputs the dataset, model and training parameters (in the form of config.yaml or cmd arguments) downloads the artifacts from wandb, creates plot and uploads to wandb

[Nesta-gitU]

I decided to instead return a dict with hessian values as a file. You can then plot them yourself how you like