feat(api): add charges list api http handler (#4103)

Author: mark-vass-konghq

api/spec/packages/aip/src/customers/charges/charges.tsp

@@ -37,6 +37,17 @@ enum ChargeStatus {
   Deleted: "deleted",
 }
 
+/**
+ * Discounts applicable to flat fee charges.
+ *
+ * This is the same as `ProductCatalog.Discounts` but without the `usage` field, which is not applicable to flat fee charges.
+ */
+@friendlyName("BillingFlatFeeDiscounts")
+@summary("Flat fee charge discounts")
+model FlatFeeDiscounts {
+  ...OmitProperties<ProductCatalog.Discounts, "usage">;
+}
+
 /**
  * Shared fields present on all customer charge responses.
  */
@@ -128,7 +139,7 @@ model ChargeBase<T extends ChargeType> {
    */
   @visibility(Lifecycle.Read)
   @summary("Price")
-  price: Shared.CurrencyAmount;
+  price: ProductCatalog.Price;
 
   /**
    * Unique reference ID of the charge.
@@ -165,7 +176,7 @@ model FlatFeeCharge {
    */
   @visibility(Lifecycle.Read, Lifecycle.Create)
   @summary("Discounts")
-  discounts?: OmitProperties<ProductCatalog.Discounts, "usage">;
+  discounts?: FlatFeeDiscounts;
 
   /**
    * The feature associated with the charge, when applicable.