feat(ecs): volume initialization rate (#34962)

### Issue # (if applicable)

None

### Reason for this change

Amazon ECS now supports for configuring Amazon EBS Provisioned Rate for Volume Initialization.

https://aws.amazon.com/jp/about-aws/whats-new/2025/05/amazon-ecs-ebs-provisioned-rate-volume-initialization/

This feature cannot be configurable by AWS CDK.

### Description of changes

- Add `volumeInitializationRate` to `ServiceManagedEBSVolumeConfiguration`

### Describe any new or updated permissions being added

None

### 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