migrate services.js to ts

src/models/exchange_rate.ts

@@ -0,0 +1,12 @@
+export interface LatestExchangeRate {
+    readonly currency: string;
+    readonly rate: string;
+}
+
+export interface LatestExchangeRateResponse {
+    readonly dataSource: string;
+    readonly referenceUrl: string;
+    readonly updateTime: number;
+    readonly baseCurrency: string;
+    readonly exchangeRates: LatestExchangeRate[];
+}