Replace ListProcessDatasets with ListProcessSets

In Arkindex 1.6.0, we are moving away from selecting datasets in dataset processes towards selecting sets of datasets. The ListProcessDatasets endpoint will be replaced by ListProcessSets, which returns each selected set as a separate result, with its associated dataset.

Thus, each dataset can be repeated multiple times. sets is replaced by set_name, with the name of the selected set, and the full list of dataset sets can be found in dataset.sets.

arkindex_worker.models.Dataset and DatasetMixin.list_process_datasets will need to be updated.

A diff of the OpenAPI schema is available.