Implementation as per the notes in the linked task (up to the hedgedoc linked in the task).
Downstream loader adaptations required to be able to ingest the output of the lister are tracked in the following diffs:
- [x] D8581: Create ContentLoader(BaseLoader) to deal with ListedOrigins with "file" visit_type
- [x] D8584: Create DirectoryLoader(BaseLoader) to deal with "integrity" field (with or without version)
Related to T3781