Update License to Match CAMELS-FR Licensing Terms

The airGRdatasets package currently adopts the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) license. However, its main data source, the CAMELS-FR dataset, is now distributed under the Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license, which does not restrict commercial use.