Function toPersistence

Returns {
    _id: string;
    createdAt: NativeDate;
    details?:
        | {
            detectedValue: number;
            limitValue: number;
            periodType?: string
            | null;
            thresholdId: string;
            thresholdName: string;
            thresholdType: string;
            utilityType: string;
        }
        | null;
    failReason?: string
    | null;
    readAt?: NativeDate | null;
    sentAt?: NativeDate | null;
    status: AlertStatus;
}

The AlertDocument ready for persistence.