Add training loss data

[pietrolesci]

Task description: "Collect all loss values into CSV files from WandB and -- if needed -- log files".

The most important file is pythia_runs.tsv in which I manually collect the run references to use in the analysis. Since I do not have visibility on how the model was trained, I am best guessing which runs are the good ones, from the many present on Wandb, for each model size and seed.

CC @oskarvanderwal @haileyschoelkopf

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