feat: Convert login button to hompage button when user is authenticated

frontend/src/app/landing-page/landing-page.component.html

@@ -1 +1,5 @@
-<button (click)="login()">Einloggen</button>
+@if (isLoggedIn) {
+    <button routerLink="/home">Zur Homepage</button>
+} @else {
+    <button (click)="login()">Einloggen</button>
+}

frontend/src/app/landing-page/landing-page.component.ts

@@ -1,16 +1,24 @@
 import { Component, inject } from '@angular/core';
 import { KeycloakService } from 'keycloak-angular';
+import {RouterLink} from "@angular/router";
 
 @Component({
   selector: 'app-landing-page',
   standalone: true,
-  imports: [],
+  imports: [
+    RouterLink
+  ],
   templateUrl: './landing-page.component.html',
 })
 export class LandingPageComponent {
+  public isLoggedIn = false;
   private keycloakService: KeycloakService = inject(KeycloakService);
 
-  login() {
+  private ngOnInit() {
+    this.isLoggedIn = this.keycloakService.isLoggedIn();
+  }
+
+  public login() {
     const baseUrl = window.location.origin;
 
     this.keycloakService.login({ redirectUri: `${baseUrl}/home` });