Add Explore 2 Climate Projections to airGRdatasets

@guillaume.thirel, I would like to suggest including climate projection datasets from Explore 2 (for one or two relevant scenarios) in the package.

These datasets could be useful for educational purposes and for studies related to climate change adaptation.
Integrating Explore 2 projections would allow users to analyze future hydrological responses across the existing pool of French catchments using consistent climate scenarios.