AWS SNS CDK: Allow referencing managed KMS keys

### Describe the feature

The CDK does not support referencing AWS managed KMS keys associated with [SNS topics](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_sns.Topic.html#properties) that have EnforceSSL set to true. This diverges from CDK behavior with S3, which [allows referencing encryption keys](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_s3.Bucket.html#encryptionkey-1) that are associated with buckets with KMS encryption enabled.

### Use Case

I would like to reference AWS managed SNS keys associated with SNS topics in the CDK. This allows for other CDK resources, such as iam policies, to reference the KMS key.

### Proposed Solution

Add a property to CDK SNS topics to return the AWS managed KMS key.

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

2.150.0

### Environment details (OS name and version, etc.)

NA

Start at the AWS SNS Topic API and compare its encryption-key behavior with the S3 encryption-key behavior described in the issue. The work is done when an SNS topic with EnforceSSL can expose its AWS-managed KMS key for use by other CDK resources, such as IAM policies.

Written by the indexing model from the issue text.