Event indicates that the server has detected the end of the user's speech
utterance and expects no additional speech. Therefore, the server will
not process additional audio (although it may subsequently return
additional results). The client should stop sending additional audio
data, half-close the gRPC connection, and wait for any additional results
until the server closes the gRPC connection. This message is only sent if
[single_utterance][google.cloud.dialogflow.cx.v3.InputAudioConfig.single_utterance] was set to
true, and is not used otherwise.