SageMaker Training Job missing TrainingImageConfig property for private Docker registry

### Describe the feature

Description:
The CDK's [SageMakerCreateTrainingJob](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_stepfunctions_tasks.SageMakerCreateTrainingJob.html#algorithmspecification) construct doesn't support the `TrainingImageConfig` property which is required when using training images from private Docker repositories.

### Use Case

Current Behavior:
When attempting to create a SageMaker training job using a private Docker image, the following configuration is required:
```
"AlgorithmSpecification": {
"TrainingImage": "${image_uri}",
"TrainingInputMode": "File",
"TrainingImageConfig": {
"TrainingRepositoryAccessMode": "Vpc"
}
}
```

However, the CDK only allows:

```
algorithmSpecification: {
trainingImage: tasks.DockerImage.fromRegistry(imageURL),
trainingInputMode: tasks.InputMode.FILE
}
```

This results in the error:
```
TrainingImageConfig with TrainingRepositoryAccessMode set to VPC must be provided when using a training image from a private Docker registry. Please provide TrainingImageConfig and TrainingRepositoryAccessMode set to VPC when using a training image from a private Docker registry.
```

### Proposed Solution

use sfn.CustomState to define the complete JSON structure manually:

```
new sfn.CustomState(this, 'TrainingJob', {
stateJson: {
Type: 'Task',
Resource: 'arn:aws:states:::sagemaker:createTrainingJob.sync',
Parameters: {
AlgorithmSpecification: {
TrainingImage: repository.repositoryUri,
TrainingInputMode: "File",
TrainingImageConfig: {
TrainingRepositoryAccessMode: "Vpc"
}
}
}
}
});
```

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

-

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

-

Start at the SageMakerCreateTrainingJob construct's algorithmSpecification entry point and compare the generated AlgorithmSpecification with the private-registry example in the issue. The work is done when callers can provide TrainingImageConfig with TrainingRepositoryAccessMode set to Vpc and the resulting training-job definition includes it.

Written by the indexing model from the issue text.