Download Amphibian dataset

The UI currently has an option to generate an "Excel" from the data loaded in the UI.

https://www.genesys-pgr.org/datasets/81bab6b6-6592-4a9d-968b-2eb1058f18cd/view shows

Ideally, the Excel file is generated by the API for the selected dataset and selected filters. The download be based on the metadata Excel template we already use (and the metadata should be populated in this download). We add two new sheets: one with raw data from Amphibian (DATA) and one where coded traits use their text labels (CODED).