Log more metrics

[JackKelly]

• Log timeseries of validation data (predicted PV over several hours, and actual PV)
• Separately, create video of the clouds for that validation sequence? Or maybe log that video to Neptune too. But don't need to re-create every run (as long as the validation data never changes)

https://docs.google.com/document/d/1E9pccSVVIfn8m14fUqBCVLWKNiU1dUe_zgTcurqLWww/edit#

[peterdudfield]

I would like to add a weighted mae / mse, where first time step is weighted a lot more heavily than the last.
The weights could exponentially decay, and the loss could be shorted to mae_exp2 = mae which weights decaying by half.

[peterdudfield]

PR: #73