aws-mwaa: add support for airflowVersion 2.11

### Describe the feature

Support 2.11 in CDK airflow versions per AWS announcement https://aws.amazon.com/about-aws/whats-new/2026/01/apache-airflow-2-11-support-amazon-managed-workflows/

### Use Case

Airflow 2.11 should make it easier for users to migrate to Airflow 3

Not yet supported https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_mwaa.CfnEnvironment.html

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

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

### AWS CDK Library version (aws-cdk-lib)

2.237.0

### AWS CDK CLI version

2.237.0

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

NA

Start with the aws-mwaa CfnEnvironment API documentation and AWS announcement linked in the issue, then trace where supported airflowVersion values are represented in the CDK implementation. Done means CDK exposes Airflow 2.11 consistently with the AWS service support and its API documentation.

Written by the indexing model from the issue text.