Use case: Flood Risk ML

[spestana]

This is a new use case that can be added to the website after some issues are resolved.

The Flood Risk ML use case does not currently launch in Binder, but does in Google Colab.

There are also a few issues related to missing data files. I think that the data preprocessing scripts that are included will generate the missing files. We may want to have examples of these files already created for the use case.