Support transcription entities bulk creation

Depends https://gitlab.com/teklia/arkindex/backend/-/issues/1459

We need a helper in the entity mixin to support this new endpoint.

Signature should look like:

create_transcription_entities(
  transcription_id="...",
  body={
    "entities": [
       {
         "name": "X",
         "type_id": "<UUID>",
         "length": 12,
         "offset": 5
       }
    ]
  }
)

The method should not support conversion from type name to type id: the goal is to be as fast as possible here.