feat(msk-alpha): support express broker for Kafka v3.9

packages/@aws-cdk/aws-msk-alpha/README.md

@@ -239,7 +239,7 @@ For more information, see [Amazon MSK Express Brokers](https://docs.aws.amazon.c
 
 **Note:** When using Express Brokers, the following constraints apply:
 
-- Apache Kafka version must be 3.6.x or 3.8.x
+- Apache Kafka version must be 3.6.x, 3.8.x, or 3.9.x
 - You must specify the `instanceType`
 - The VPC must have at least 3 subnets (across 3 AZs)
 - `ebsStorageInfo` is not supported

packages/@aws-cdk/aws-msk-alpha/lib/cluster.ts

@@ -530,11 +530,12 @@ export class Cluster extends ClusterBase {
 
     if (isExpress) {
       // Validate Kafka version compatibility
-      const supportedVersions = ['3.6', '3.8'];
+      // express broker documentation for supported versions https://docs.aws.amazon.com/msk/latest/developerguide/msk-broker-types-express.html#msk-broker-types-express-notes
+      const supportedVersions = ['3.6', '3.8', '3.9'];
       const kafkaVersionString = props.kafkaVersion.version;
       const isCompatibleVersion = supportedVersions.some(version => kafkaVersionString.includes(version));
       if (!isCompatibleVersion) {
-        throw new core.ValidationError(`Express brokers are only supported with Apache Kafka 3.6.x and 3.8.x, got ${kafkaVersionString}`, this);
+        throw new core.ValidationError(`Express brokers are only supported with Apache Kafka ${supportedVersions.join(', ')}, got ${kafkaVersionString}`, this);
       }
 
       if (!props.instanceType) {

packages/@aws-cdk/aws-msk-alpha/test/cluster.test.ts

@@ -1106,7 +1106,7 @@ describe('MSK Cluster', () => {
           ),
           brokerType: msk.BrokerType.EXPRESS,
         });
-      }).toThrow('Express brokers are only supported with Apache Kafka 3.6.x and 3.8.x, got 2.6.1');
+      }).toThrow('Express brokers are only supported with Apache Kafka 3.6, 3.8, 3.9, got 2.6.1');
     });
   });
 });