update: add missing copyright notice and license information to CmabClientHelper

Author: FarhanAnjum-opti

core-api/src/main/java/com/optimizely/ab/cmab/client/CmabClientHelper.java

@@ -1,3 +1,18 @@
+/**
+ * Copyright 2025, Optimizely
+ *
+ * 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
+ *
+ * https://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.
+ */
 package com.optimizely.ab.cmab.client;
 
 import java.util.Map;