bug: algorithm output does not indicate when it has encountered transient error conditions

[garobrik]

Description

Currently when the algorithm encounters a transient error (e.g. SoilWeb API timeout) it logs an error and then tries a fallback API, which might return less accurate data. We should communicate what happened in the algorithm's output so that downstream clients can decide whether/how to retry.

Additional context

This can be triggered reliably by querying coordinates which don't have data (e.g. NOTCOM), like this coordinate pair:

{"lat": 34.92816, "lon": -114.80764}

But could happen for any coordinate due to transient network issues, which could result in suboptimal data being stored in a cache.