OZG-5176 OZG-5227 Add unavailable page component

alfa-client/apps/admin/src/pages/unavailable/unavailable-page/unavailable-page.component.html

+<p class="mb-2 block font-bold">Die Administrations-Oberfläche ist nicht verfügbar.</p>
+
+<p>
+  Prüfen Sie, ob folgendes zutrifft:<br />
+  Ihnen ist die Rolle Admin_Admin zugewiesen.<br />
+  Bitte bei der verantwortlichen Person des User-Managements bzw. des Keycloaks melden.<br />
+</p>

alfa-client/apps/admin/src/pages/unavailable/unavailable-page/unavailable-page.component.spec.ts

+import { ComponentFixture, TestBed } from '@angular/core/testing';
+import { UnavailablePageComponent } from './unavailable-page.component';
+
+describe('UnavailablePageComponent', () => {
+  let component: UnavailablePageComponent;
+  let fixture: ComponentFixture<UnavailablePageComponent>;
+
+  beforeEach(async () => {
+    await TestBed.configureTestingModule({
+      declarations: [UnavailablePageComponent],
+    }).compileComponents();
+
+    fixture = TestBed.createComponent(UnavailablePageComponent);
+    component = fixture.componentInstance;
+    fixture.detectChanges();
+  });
+
+  it('should create', () => {
+    expect(component).toBeTruthy();
+  });
+});

alfa-client/apps/admin/src/pages/unavailable/unavailable-page/unavailable-page.component.ts

+import { Component } from '@angular/core';
+
+@Component({
+  selector: 'unavailable-page',
+  templateUrl: './unavailable-page.component.html',
+  styles: [],
+})
+export class UnavailablePageComponent {}