refactor: use constant for api url

frontend/src/app/feature/game/dice/dice.service.ts

@@ -2,12 +2,13 @@ import { Injectable } from '@angular/core';
 import { HttpClient } from '@angular/common/http';
 import { Observable } from 'rxjs';
 import { DiceDto, DiceResult } from './dice.model';
+import {environment} from "@environments/environment";
 
 @Injectable({
   providedIn: 'root',
 })
 export class DiceService {
-  private apiUrl = '/backend/dice';
+  private apiUrl = `${environment.apiUrl}/dice`;
 
   constructor(private http: HttpClient) {}