Add WorkerRun model

The model should be a M2M through model between WorkerVersion and DataImport.

It must have a List Field of UUID to list the WorkerRun parents.

A unique_together limits worker_version per data_import

classDiagram
  DataImport <|-- WorkerRun
  WorkerRun <|-- WorkerVersion

  class WorkerRun {
   parents: List(WorkerRun UUID)
   unique(worker_version, data_import)
  }

This model should be exposed in the admin as an inline on DataImport