This 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 was set to true, and is not used otherwise.
PartialDtmfDigits
Message contains DTMF digits. Before a message with DTMF_DIGITS is sent,
a message with PARTIAL_DTMF_DIGITS may be sent with DTMF digits collected
up to the time of sending, which represents an intermediate result.