feat: Add GET handler to Payment Service (#3)

Implement and test a GET handler in the Payment Service, allowing CH services to use this SDK to retrieve pre-existing payment sessions from the CH Payment API.

Author: rhysbarrett

dist/services/payment/service.d.ts

@@ -16,5 +16,12 @@ export default class PaymentService {
    * @param createPaymentRequest a create payment request
    */
     createPaymentWithFullUrl(createPaymentRequest: CreatePaymentRequest): Promise<ApiResult<ApiResponse<Payment>>>;
+    /**
+   * Retrieves a payment session.
+   *
+   * @param paymentResourceUri the desired payment session's URI
+   */
+    getPayment(paymentResourceUri: string): Promise<ApiResult<ApiResponse<Payment>>>;
     private createPaymentHandler;
+    private handlePaymentHttpResponse;
 }