Fix e2e regression caused by changes in AuthService

Previously, a PR introduced new method signatures in AuthService.
However, these were not introduced in MockAuthService, causing 
the testing environment to fail when the application encountered these
undefined method signatures.

Lets address this regression by adding the method signatures for these
methods.

src/app/core/services/mocks/mock.auth.service.ts

@@ -98,4 +98,14 @@ export class MockAuthService {
   startOAuthProcess() {
     this.accessToken.next('FabricatedToken');
   }
+
+  navigateToLandingPage() {
+    this.router.navigateByUrl(this.phaseService.currentPhase);
+  }
+
+  clearNext() {}
+
+  getNext() {}
+
+  storeNext(next: any) {}
 }