Ensure that AWS SNS topic is encrypted using AWS managed CMKs (Customer Master Key) instead of AWS-owned CMK's

AWS SNS topic should be encrypted using AWS Managed Customer Master Key (CMK), instead of AWS-owned CMK. This is required in order to meet encryption regulatory requirements of Server-Side encryption for sensitive data that may be stored in the topic. In addition, encrypting SNS topic with AWS-managed CMK allows you to view the CMK and its key policy and also audit the encryption/decryption events by examining the SNS API calls using CloudTrail.