Adjust `end of speech` timeout on streaming speech to text

**What component of `google-cloud-cpp` is this feature request for?**

google/cloud/speech/speech_client

**Is your feature request related to a problem? Please describe.**

I would like to reduce timeout it takes on Google before end of speech is detected

**Describe the solution you'd like**

I would like to have parameter added to streaming recognition config (speech::v1::StreamingRecognizeRequest) that would setup this timeout, similarly to what EndSilenceTimeout is on MSFT (https://learn.microsoft.com/en-us/windows/apps/design/input/set-speech-recognition-timeouts)

> End Silence Timeout:
> This timeout is triggered after a phrase has been successfully recognized, and the service waits for further speech input before finalizing the recognition result.
> The EndSilenceTimeout property determines how long the service waits for additional speech after a recognized phrase before concluding that the speech input has ended.
> This timeout can be adjusted to accommodate various speaking styles, allowing for short pauses within a longer phrase without prematurely ending the recognition.

**Describe alternatives you've considered**

No alternatives are known to exist, but please let me know otherwise

**Additional context**

Request originates from work on AI voice assistants where I would like to experiment with slightly reduced end of speech timeouts

Bắt đầu với google/cloud/speech/speech_client và định nghĩa API speech::v1::StreamingRecognizeRequest, sau đó kiểm tra xem Google Speech-to-Text có cung cấp timeout có thể cấu hình cho thời điểm kết thúc lời nói hay không. Hoàn thành khi có thể cấu hình một timeout được hỗ trợ cho nhận dạng streaming và hành vi của nó được xác minh bằng một bài kiểm thử phù hợp.

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