API should pull from Edge for recent data, and FDSN for older
The backend currently pulls any data from one factory, even if that one factory depends on the channel or time resolution ("interval") requested
- modify so that, for variometer data, it also consider absolute time
- variometer data reside on the Edge server for a limited time (days? weeks?)
- pull from Edge for the current day (or maybe "today" and "yesterday"), but then
- pull from FDSN for older data