Transformer.transform() doesn't return job name

**Describe the feature you'd like**

Get name of batch transform job after `sagemaker.transformer.Transformer.transform()` call, because the method does **not** return anything.

**How would this feature be used? Please describe.**

Job name will be used for bookkeeping purposes. Job name will be used to locate logs if debugging is required.

**Describe alternatives you've considered**

When `transform` method is executed, it sets the object field `latest_transform_job`. We are planning to use `transformer. latest_transform_job.name` to get the job name.

But the `Transformer` documentation doesn't mention anything about the field `latest_transform_job`. We are not sure if the field is safe for use or if the field will get removed/replaced in the future versions.

**Additional context**
* https://github.com/aws/sagemaker-python-sdk/blob/dev/src/sagemaker/transformer.py#L210
* https://sagemaker.readthedocs.io/en/stable/api/inference/transformer.html