docs: GenAI - update comments in GenerationConfig property

PiperOrigin-RevId: 681595419

Author: vertex-sdk-bot

vertexai/generative_models/_generative_models.py

@@ -1605,11 +1605,12 @@ def __init__(
 
  - ``text/plain``: (default) Text output.
  - ``application/json``: JSON response in the candidates.
+ - ``text/x.enum``: enum response in the candidates. Only valid when
+ response_schema is provided.
 
  The model needs to be prompted to output the appropriate
  response type, otherwise the behavior is undefined.
- response_schema: Output response schema of the genreated candidate text. Only valid when
- response_mime_type is application/json.
+ response_schema: Output response schema of the genreated candidate text.
  routing_config: Model routing preference set in the request.
  logprobs: Logit probabilities.
  reponse_logprobs: If true, export the logprobs results in response.