Add quantile-quantile plot to wandb custom charts

[lm2612]

Pull Request

Description

Addresses issue #538
It would be useful to compare p-levels as well as the median on W&B. We can do this using a quantile-quantile plot, which would show the true p-level on the x-axis against the fraction of validation data that falls below that p-level on the y-axis. The ideal model would line up along the y=x line.

To do this I have used the existing line plotting function that plots the MAE at different horizons. This involves storing the fraction of the validation data below each level in a wandb table. I've extended the function wandb_line_plot() to also include the option to show the identity line where y=x between 0 and 1.

How Has This Been Tested?

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• Yes

Checklist:

• My code follows OCF's coding style guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked my code and corrected any misspellings