add possibility to finish a goal (#90)

closes #67

Reviewed-on: #90

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

@@ -30,4 +30,8 @@ export class AllowanceService {
     deleteAllowance(allowanceId: number, userId: number) {
         this.http.delete(`${this.url}/user/${userId}/allowance/${allowanceId}`).subscribe();
     }
+
+    completeGoal(goalId: number, userId: number) {
+        this.http.post(`${this.url}/user/${userId}/allowance/${goalId}/complete`, {}).subscribe();
+    }
 }