v14.4.0a4

• #1734 Update generated code for private-preview
  • ⚠️ Add support for new value spend_threshold on enums Billing.Alert.alert_type, billing.AlertCreateParams.alert_type, and billing.AlertListParams.alert_type
  • Add support for spend_threshold on Billing.Alert and billing.AlertCreateParams
  • Add support for invoice_item, proration_details, proration, and subscription on InvoiceLineItem.Parent.ScheduleDetail
  • Add support for custom on PaymentMethodModifyParams
  • Add support for payment_method_reference and usage on PaymentMethod.Custom
  • Add support for outstanding_usage_through and unused_time_from on SubscriptionPauseParamsBillFor
  • ⚠️ Remove support for outstanding_usage and unused_time on SubscriptionPauseParamsBillFor
  • ⚠️ Remove support for payment_behavior on SubscriptionResumeParams

See the changelog for more details.