[Epic] Consolidate ProgressReporting into a single model so it's simpler for plugin writers
Currently the pulpcore.app.models.progress module provides three objects:
These are confusing for plugin users and should be combined.
Delete ProgressBar and ProgressSpinner, and consolidate them into a single model. In the database they are already a single model since ProgressBar and ProgressSpinner are proxy models for ProgressReport.
This will be a plugin API breaking change and needs to be advertised to pulp-dev and also come with a fix for pulp_file.