The top-level message sent by the client for the StreamingRecognize
method. Multiple StreamingRecognizeRequest messages are sent. The
first message must contain a streaming_config message and must not
contain audio data. All subsequent messages must contain audio
data and must not contain a streaming_config message.
Provides information to the recognizer that specifies how to
process the request. The first StreamingRecognizeRequest
message must contain a streaming_config message.