PurpleAir changed their API; adapt to new calls

[jywarren]

They dropped the /data.json style calls a little before?: https://community.purpleair.com/t/discontinuation-of-the-json-and-data-json-urls/713/2

We had expected this format: https://github.com/publiclab/leaflet-environmental-layers/blob/main/cypress/fixtures/purpleMarker.json

But the new format is: https://map.purpleair.com/v1/sensors?token=8f2O5WHWva0Imrp7rEB2AmfHd41SMiFuCYStIXV52vk%2BBKHCpds8v0dGdXDyXNuwztL6jzbw6GDwX6vqk8DDtxIUSj8%2BsFjwGBLzK8T1q1p0pI%2BTTDw11mD3qFdzgIw2&fields=is_owner,name,location_type,latitude,longitude,altitude,last_seen,channel_state,channel_flags,confidence,primary_key_a,pm2.5_10minute&max_age=604800&nwlat=41.91210058954218&selat=41.73377525046183&nwlng=-71.59125291137713&selng=-71.23934708862353

Originally posted by @jywarren in #668 (comment)

(unrelated - support for changes to historical API here; not the same API: https://community.purpleair.com/t/purpleair-data-migration-to-bigquery-and-a-new-api/295)