Generate Dummy Data for Step Based on Specification

[kahboom]

As a user, I would like to be able to predict the output of an integration up to a particular Step or series of Steps by seeing their output using dummy data based on their specification, which would help test the execution of those Steps as a form of debugging.

Use cases:

• Improving the general developer experience, debugging assistance
• Easier planning of integrations
• Generating data for previewing custom views, or Step Extensions
• Generating data to be used for testing

[Delawen]

Can this be useful for #253 ?