New sample: simple batch processing

[feuzeu]

What was changed

A new sample workflow is added.

Why?

The new sample highlights a new use case for Temporal. See the Readme in the example directory for more information.

Checklist

1. Closes New sample proposal: parallel batch processing #65

2. How was this tested:
   Following the other examples, this one provides one cli command to start a workflow, and another one to query its status.

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