Add license header to ClientOptionsTest.java

- Add required OpenSearch Contributors license header
- Fixes license header violation in new test file

Signed-off-by: Aiswarya Sadananda Rao <aiswarao@amazon.com>

Author: Aiswarya Sadananda Rao

data-prepper-plugins/aws-lambda/src/test/java/org/opensearch/dataprepper/plugins/lambda/common/config/ClientOptionsTest.java

@@ -1,3 +1,8 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 package org.opensearch.dataprepper.plugins.lambda.common.config;
 
 import org.junit.jupiter.api.Test;