Expand docs for freshness-anomalies

[eraliod]

Path: /guides/anomaly-detection-tests/freshness-anomalies

The documentation for freshness_anomalies has no explanation or examples for 2 of its listed parameters:

where_expression: sql expression
anomaly_sensitivity: int

While the sql expression is more intuitive and can be tested. Users could use an explanation or example what anomaly_sensitivity does.