expiring endpoint now includes cert_expiry and plan_expiry

The expiring endpoint will now include additional parameters

plan_expiry - This will indicate when the plan will expire for the product. For certificates this means the date up to which certificates can be reisued at no additional charge

cert_expiry - This will indicate the date the current live certificate on the plan will expire. The certificate should be reissued or renewed before this date.

The order_expiry parameter is being deprecated and developers should move away from using this.

This update is to assist customers using the API to manage certificates as the maximum certificate lifetimes are reducing.