(stepfunctions-tasks): Sagemaker StartPipelineExecution

### Describe the feature

I need to call Sagemaker's StartPipelineExecution API. But this is missing in aws_stepfunctions_tasks.

### Use Case

I need to call Sagemaker's StartPipelineExecution API. There is a StartPipelineExecution action in Step Functions Workflow UI. But this is missing in aws_stepfunctions_tasks.

### 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

### CDK version used

2.28.1 (build d035432)

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

macOS Monterey 12.3.1 (21E258)

Start by locating the aws_stepfunctions_tasks implementation and existing SageMaker task patterns, then compare them with the StartPipelineExecution API and the Step Functions Workflow UI action. Done means the missing task can invoke that API through the CDK Step Functions tasks package, with the relevant tests updated or added.

Written by the indexing model from the issue text.