Use cases for associating real data with a DGP or an Experiment

[jpdunc23]

If the user wants to use their own real data, they currently have to have that data in the global environment and use directly in the dgp_fun with future.globals, pass in as an argument to the dgp_fun, or load from disk directly from the dgp_fun. This issue is to consider alternatives for associating real data with a DGP or Experiment. Some ideas/issues to consider:

• Pass in as an argument to add_dgp() or create_experiment()
• Have data be a field of the DGP or Experiment class. Less flexible because then you're stuck with that data for the DGP unless we include a data_list field.
• Should the user pass a path to the data or the data obj. itself? Or allow both?