Add allowance service and create get endpoint for allowance

frontend/allowance-planner-v2/src/app/services/allowance.service.ts

@@ -0,0 +1,17 @@
+import { HttpClient } from '@angular/common/http';
+import { Injectable } from '@angular/core';
+import { Observable } from 'rxjs';
+import { Allowance } from '../models/allowance';
+
+@Injectable({
+    providedIn: 'root'
+})
+export class AllowanceService {
+    private url = 'http://localhost:8080/api';
+
+    constructor(private http: HttpClient) {}
+
+    getAllowanceList(userId: number): Observable<Array<Allowance>> {
+        return this.http.get<Allowance[]>(`${this.url}/user/${userId}/allowance`);
+    }
+}