The bulk classifications endpoint allows creating duplicates

https://sentry.io/organizations/teklia/issues/1717529772/

It is possible to create duplicate Classification instances, causing 500 errors for unique constraint violations:

cli.request('CreateClassifications', body={
    'parent': '16c31919-0a50-4a0c-aa83-f12123f5a549',
    'classifier': 'dummy',
    'classifications': [
        {'class_name': 'something', 'confidence': 1},
        {'class_name': 'something', 'confidence': 0.5}
    ]
})

arkindex.documents.serializers.ml.ClassificationsSerializer could easily check for duplicate class names and cause HTTP 400.