aws-sagemaker-alpha: Add ContainerStartupHealthCheckTimeoutInSeconds to InstanceProductionVariantProps

### Describe the feature

In `aws-sagemaker-alpha` package, the `InstanceProductionVariantProps` interface should have `ContainerStartupHealthCheckTimeoutInSeconds`.

- SM API Docs: https://docs.aws.amazon.com/sagemaker/latest/APIReference/API_ProductionVariant.html#sagemaker-Type-ProductionVariant-ContainerStartupHealthCheckTimeoutInSeconds

- CFN SM Docs: https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-properties-sagemaker-endpointconfig-productionvariant.html#cfn-sagemaker-endpointconfig-productionvariant-containerstartuphealthchecktimeoutinseconds

### Use Case

Configure ContainerStartupHealthCheckTimeoutInSeconds for an SM Endpoint

### 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)

2.214.0

### AWS CDK CLI version

2.1026.0 (build ad1a7ce)

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

Amazon Linux 2

Locate the aws-sagemaker-alpha package and its InstanceProductionVariantProps interface, then read the surrounding property definitions and related tests if present. Use the linked SageMaker and CloudFormation API documentation to confirm the property type and naming; done means users can configure ContainerStartupHealthCheckTimeoutInSeconds for an SM Endpoint.

Written by the indexing model from the issue text.