add: HTTP request samples for Payment API (v1) including payment and callback scenarios

Author: yeonjiyeon

http/commerce-api/payment-v1.http

@@ -0,0 +1,26 @@
+### 결제 요청
+POST {{commerce-api}}/api/v1/payments
+X-USER-ID: 1
+Content-Type: application/json
+
+{
+  "orderId": 12345,
+  "cardType": "CREDIT",
+  "cardNo": "1111-2222-3333-4444",
+  "amount": 50000
+}
+
+###
+
+### 결제 콜백
+POST {{commerce-api}}/api/v1/payments/callback
+Content-Type: application/json
+
+{
+  "transactionKey": "tx_20251205_0001",
+  "orderId": "12345",
+  "status": "SUCCESS",
+  "reason": null
+}
+
+###