New models to support the new logic for Workflows

[Tansito]

Summary

This PR implements the main required changes in the DB to support the new functionality around Workflows.

The main changes are:

• A new ProgramStep model where will live the definition of the different steps of the Function
• A new Workflow model where we will instantiate the Function and the generated Jobs to execute the Workflow
• Job table is modified to support the reference to Workflow and other jobs as dependencies

The relationships between these new entities would be:

• A Program can contain a set of ProgramSteps
• Steps can depends on another steps as a way to draw a dependency graph
• A Program will generate multiple Workflows and a Workflow can only be owned by one function
• A Workflow it's a way to groups jobs but Job doesn't need to be managed by a Workflow specifically