MSK::Cluster Should Make BootstrapServers Available As A Return Value

### Name of the resource

AWS::MSK::Cluster

### Resource name

_No response_

### Description

The existing AWS:MSK::Cluster resource only makes its ARN available as a [return value](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-msk-cluster.html#aws-resource-msk-cluster-return-values).

To do anything useful with the MSK Cluster, you need to be able to return the list of bootstrap servers for which there is an [API](https://docs.aws.amazon.com/msk/1.0/apireference/clusters-clusterarn-bootstrap-brokers.html#GetBootstrapBrokers).

I would like to be able to get the list of bootstrap servers so that I could use them in other CloudFormation resources. Specifically, I need to be able to feed it into a new MSK Connector resource which requires the list of [bootstrap servers](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-kafkaconnect-connector-apachekafkacluster.html#cfn-kafkaconnect-connector-apachekafkacluster-bootstrapservers).

### Other Details

_No response_

Start with the AWS::MSK::Cluster return-values documentation and the GetBootstrapBrokers API linked in the issue. The work is done when the cluster exposes its bootstrap server list as a return value that other CloudFormation resources can consume, including an MSK Connector.

Written by the indexing model from the issue text.