feat(docdb): i/o optimized storage type (#30163)

### Issue # (if applicable)

Closes #30165.

### Reason for this change

Document DB can use I/O optimized storage type but CDK cannot configure that.

### Description of changes

Add `storageType` to `ClusterProps`.

### Description of how you validated changes

Add both unit and integ tests.

### 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: badmintoncryer