Changes to Fetch a Subscription

added the optional property end_subscription_at to the response with the 200 status

added the optional property has_usage_based_plan to the response with the 200 status

the response property expires_at became nullable for the status 200

the response property subscription_details/discount_phase_details became nullable for the status 200

the response property subscription_details/trial_details became nullable for the status 200

the response property subscription_plan_id became nullable for the status 200

the response property total_billing_intervals became nullable for the status 200

the response property nickname became nullable for the status 200