New label detection model An improved model is now available for Label Detection

## Change **New label detection model** An improved model is now available for Label Detection. Along with the improved model, the [topicality](https://cloud.google.com/vision/docs/reference/rpc/google.cloud.vision.v1#entityannotation) field is now populated correctly. Specify "`builtin/latest`" in the model field of a `Feature` object to use the new model. We'll support both the current model and the new model the next 90 days. After 90 days, the new models will become the default. The current models can still be accessed by specifying "`builtin/legacy`" for an additional 90 days before they are deprecated.