[aws-stepfunctions-tasks] Add support for SageMaker Processing

SageMaker and Step Functions released a new integration to create processing jobs directly in the state machine:
- https://docs.aws.amazon.com/step-functions/latest/dg/connect-sagemaker.html#sagemaker-example-processing
- https://docs.aws.amazon.com/sagemaker/latest/APIReference/API_CreateProcessingJob.html

### Use Case

SageMaker Processing is a very flexible API call that can be used to run preprocessing/post-processing and therefore fully automate a ML use case using Step Functions.

### Proposed Solution

Use https://github.com/aws/aws-cdk/blob/master/packages/%40aws-cdk/aws-stepfunctions-tasks/lib/sagemaker/create-training-job.ts as starting point.

### Other

* [ ] :wave: I may be able to implement this feature request

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This is a :rocket: Feature Request