Fix Job implementation for use of model_request attribute's output_formats

[robertbartel]

The Job class is implemented with a model_request property of hinted type ExternalRequest. There are calls in a couple of places in python/services/dataservice/dmod/dataservice/service.py to job.model_request.output_formats, but ExternalRequest does not have an output_formats attribute/property.

This property is actually defined in DmodJobRequest. It seems that most use cases for the data service have involved model_request objects that are both ExternalRequest and DmodJobRequest, but this needs to be either guaranteed/asserted or the design needs to be properly generalized.