Add optional confidence

Related to issue #805 (closed)

The confidence field is present on endpoints CreateTranscriptionEntity and ListTranscriptionEntities. If not provided, it defaults to "null". Valid values are floats between 0 and 1.

This will be useful for NER models that outputs confidence score for entities. In the future we will also be able to filter entities based on this score.

arkindex/documents/api/entities.py

@@ -232,7 +232,7 @@ class TranscriptionEntityCreate(CreateAPIView):
     serializer_class = TranscriptionEntitySerializer
     # For OpenAPI type discovery: a transcription's ID is in the path
     queryset = Transcription.objects.none()
-    
+
     def get_serializer_context(self):
         context = super().get_serializer_context()
         if not self.request: