FR-13012 - support-angular-16-signals

[yuvalotem1]

Support angular 16 signals with backward compatibility

• create v16 folder signals file that handle signals backward compatibility
• create new signals functions wrapping all of our observables with toSignal
• refactor frontegg-app.service and frontegg-auth.service - split into files

Example usage of signals

app.component.ts
export class AppComponent {
  isLoading: Signal<boolean | undefined>

  constructor(private fronteggAppService: FronteggAppService) { }
  this.isLoading = this.fronteggAppService.isLoadingSignal;
}

app.component.html
<div *ngIf="!isLoading()">
  <router-outlet></router-outlet>
</div>