fetch item prices - throttle end points with promise queue

app/model/item-price.ts

@@ -0,0 +1,14 @@
+export interface IItemPrice {
+  currency_rec: string;
+  data: any;
+  error: number;
+  item_base: string;
+  max_price: string;
+  median_price: string;
+  min_price: string;
+  name: string;
+  pred_explanation: any[];
+  recommendedPrice: string;
+  resultsCounted: number;
+  status: number;
+}