Extend data processor and allow data type override.

[davner]

Addresses #1124

This extends the run_data_processor function by adding an optional parameter that allows overriding the data product type. This will enable selecting a specific processor at runtime.

[jchate6]

How do you see this feature being used?
Should we add optional fields to the form or api_views to give users access to this?

Should we add a section in the customizing data processing docs explaining how to use this feature?