AlertEvaluation

Evaluation cadence. {@code intervalSeconds} must be one of {30, 60, 120, 300, 600, 900, 1800, 3600}; {@code pendingDurationSeconds} and {@code recoveryDurationSeconds} must be multiples of {@code intervalSeconds}. A duration of 0 means fire/clear immediately with no delay. On UpdateAlert a supplied evaluation block is replaced whole, not merged: an omitted {@code pendingDurationSeconds} or {@code recoveryDurationSeconds} is cleared to unset (no such duration), not preserved and not defaulted to 0. {@code intervalSeconds} is required whenever the block is present. All enforced server-side / by the front-door validator.