Terra: Distinguish between google storage and azure buckets

[bwalsh]

https://github.com/anvilproject/drs_downloader/pull/15/files/4213252f7947b315b723308d71759052c668eb3c#r1051642768

This potentially involves authentication (how the user identifies themselves - currently gcloud print auth token)
We also need to confirm how this might be deduced from the martha endpoint.