Data Sourcing and Transformations: add jsonpath as possible transform

# Summary
Add the ability to use jsonpath as part of the data transform step

# Use Cases
1. You input some structured json data either from an external source, or from a previous step's artifact in the workflow.
2. You want to filter, map, or select a specific value from the json so you can pass it to a job downstream, without having to write a bash script.
I looked briefly at expr and the existing example for data sourceing, and I couldn't find a way to achieve my use case (specifically selecting a single value from an artifact json generated in a previous step).
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**Message from the maintainers**:

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Start by reading the existing data-sourcing example and the current expr-based transform support to understand how workflow artifacts are transformed. The work is done when structured JSON can be filtered, mapped, or queried with jsonpath and the selected result can be passed to a downstream job without a bash script.

Written by the indexing model from the issue text.