Add placeholder Credentials.swift file

Author: andrewheard

FirebaseVertexAI/Tests/TestApp/Tests/Integration/Credentials.swift

@@ -0,0 +1,29 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import Foundation
+
+// Copy the Google-internal file from:
+// https://source.corp.google.com/piper///depot/google3/third_party/firebase/ios/Secrets/VertexAI/TestApp/Tests/Integration/Credentials.swift
+//
+// Alternatively, set up emails / passwords in Firebase Auth for a custom Firebase project.
+enum Credentials {
+  // Auth User 1
+  static let emailAddress1 = ""
+  static let emailPassword1 = ""
+
+  // Auth User 2
+  static let emailAddress2 = ""
+  static let emailPassword2 = ""
+}