request add an example for use case

Request to add an example for a multi-region CMK keys use case in a schema linking and cluster linking environment.

For instance, consider two Kafka clusters with bidirectional cluster linking enabled that share the same schema registry. These two clusters, located in different regions, operate within the same Confluent Cloud (CC) environment. Through cluster linking, the topics in these clusters share the same schema subjects. Additionally, the topics in the two clusters have different prefixes.