feat(rds): support zero ACU for Aurora Serverless V2 (#32231)

### Issue # (if applicable)

Closes #32234.

### Reason for this change
Amazon Aurora Serverless v2 supports scaling to zero capacity.

Ref: https://aws.amazon.com/about-aws/whats-new/2024/11/amazon-aurora-serverless-v2-scaling-zero-capacity/



### Description of changes
"Updated validation to permit zero as a value for `serverlessV2MinCapacity`.



### Description of how you validated changes
Fix unit tests and add an integ test.



### 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)

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: mazyu36