Fix annotation data type coersion by Pydantic

[whistler]

When creating a Label, the annotation data type class was being changed and the global_key field was disappearing. Example:

label = []
label.append(
  lb_types.Label(
    data=lb_types.ConversationData(
      global_key=global_key
    ),
    annotations=[
      ner_annotation
    ]
  )
)

Output

[Label(uid=None, data=VideoData(file_path=None,frames=None,url=None), annotations=[ObjectAnnotation(confidence=None, name='ner', feature_schema_id=None, extra={}, value=ConversationEntity(start=0, end=8, extra={}, message_id='4'), classifications=[])], extra={})]

The problem was that Pydantic tries to coerce objects to the first class listed in a Union. See Pydantic docs for more details.

This is fixed by adding a discriminator field (class_name) which is ignored during serialization.

[kopreschko]

small typo here, coersion => coercion

[whistler]

Good catch! fixed!

[kopreschko]

awesome work BTW!

[kkim-labelbox]

should this be class_name?

[whistler]

good catch! fixed it.

[vbrodsky]

is this a generic pydantic type? sorry pydantic documentation links do not work for me for some reason

[whistler]

I've defined this type on line 19 above since the list was getting too long.

[vbrodsky]

Fantastic, we should extend it to all our union types... as you know they are all susceptible