### Issue # Closes #35199. ### Reason for this change Adding support for DocumentDB [serverless clusters](https://docs.aws.amazon.com/documentdb/latest/developerguide/docdb-serverless.html) ### Description of changes Added the new `ServerlessV2ScalingConfiguration` property which maps to the corresponding [CFN property](https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-properties-docdb-dbcluster-serverlessv2scalingconfiguration.html). `instanceType` is no longer a required field, since a serverless cluster has no instance type. This is not a breaking change since loosening constraints does not impact existing users. The choice of `instanceType` or `serverlessV2ScalingConfiguration` aligns with the AWS console experience of choosing between the two when creating a cluster. <img width="1125" height="409" alt="Screenshot 2025-09-25 at 14 20 27" src="https://github.com/user-attachments/assets/c7b94897-e1f2-40d3-b785-1204c4a27c6b" /> <img width="1625" height="495" alt="Screenshot 2025-09-25 at 14 20 34" src="https://github.com/user-attachments/assets/9f8eb14a-ef0b-4f52-85d3-09a199113259" /> ### Describe any new or updated permissions being added N/A ### Description of how you validated changes ### Checklist - [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md) ---- *By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*