Simplify and document actual information returned to the loader
This is a breaking change which needs adaptation in the deposit loader (D4105).
This moved the provider, tool and raw_metadata keys to the top-level.
(origin in the end is still used by the loader when flushing the metadata in the revision...)
The main reason is to cleanup. Took the opportunity since I need a deployment for !388 (closed) anyways.
Related to #2649 (closed)
Test Plan
tox
Migrated from D4101 (view on Phabricator)