Feature request: allowing for Retry to work with SageMaker steps

Currently, the `Retry` mechanism does not work with `TrainingStep `and `ProcessingStep` as the full job name must be specified to the step constructor so that if the step fails when the job has already been created, all retries will fail in submitting the job as the job name has already been used.
This happens for almost any error (including capacity errors) excluding throttling errors.

A possible solution might be to add an alternative parameter to specify a job name prefix, instead of a full name, and let SageMaker add some random suffix.