auth: fixes unit and e2e tests

adds MockAuthGuard which always return user 'hardcoded'

Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/auth/mock-auth.guard.ts

@@ -0,0 +1,18 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { ExecutionContext, Injectable } from '@nestjs/common';
+
+@Injectable()
+export class MockAuthGuard {
+  canActivate(context: ExecutionContext) {
+    const req = context.switchToHttp().getRequest();
+    req.user = {
+      userName: 'hardcoded',
+    };
+    return true;
+  }
+}