feat(FE-212): implement PurchaseApi service for purchase requests

src/services/api/purchasing.ts

@@ -0,0 +1,12 @@
+import { BaseApiService } from './base';
+import {
+  CreatePurchasePayload,
+  Purchase,
+  UpdatePurchasePayload,
+} from '@/types/api/purchasing/purchasing';
+
+export const PurchaseApi = new BaseApiService<
+  Purchase,
+  CreatePurchasePayload,
+  UpdatePurchasePayload
+>('/purchase-requests');