Provide guidance on creating a header for `streaming_synthesize` in streaming_tts_quickstart.py

From https://github.com/googleapis/google-cloud-python/issues/13405, the response to `streaming_synthesize` is `headerless LINEAR16 audio with a sample rate of 24000.`. The code sample below prints the size of the audio content but does not include the necessary header to actually play the audio.

https://github.com/GoogleCloudPlatform/python-docs-samples/blob/5e8e1788598a22f4dc7ceb13b0d62ef373406554/texttospeech/snippets/streaming_tts_quickstart.py#L46-L48

This may not be the purpose of the code sample, however having this extra information in the code sample will help with debugging customer issues such as https://github.com/googleapis/google-cloud-python/issues/13405.

I added code which includes the raw audio header, however there is likely an easier way to achieve this. We should provide guidance on how folks should create the audio header.

```
# This is a raw header based on the spec at https://docs.fileformat.com/audio/wav/
header = b'RIFF\x00\x00\x00\x00WAVEfmt \x10\x00\x00\x00\x01\x00\x01\x00\xc0]\x00\x00\x80\xbb\x00\x00\x02\x00\x10\x00data\x00\x00\x00\x00'

total_length = 0

with open(f"output.wav", "wb") as out:
out.write(header)
for response in streaming_responses:
# calculate the length of the content
total_length += len(response.audio_content)
out.write(response.audio_content)
# Position 40 - 43: Size of the data section
out.seek(40)
out.write(bytes([total_length & 0xFF, (total_length >> 8) & 0xFF, (total_length >> 16) & 0xFF, (total_length >> 24) & 0xFF]))

import os
file_size = os.path.getsize("output.wav")

with open(f"output.wav", "r+b") as out:
# Position 4-7: Size of the overall file - 8 bytes, in bytes (32-bit integer). Typically, you’d fill this in after creation.
out.seek(4)
out.write(bytes([file_size & 0xFF, (file_size >> 8) & 0xFF, (file_size >> 16) & 0xFF, (total_length >> 24) & 0xFF]))
```

從 texttospeech/snippets/streaming_tts_quickstart.py 第 46-48 行附近開始，並檢視連結的 WAV 規格。確定應如何為不含 header 的 24,000 Hz LINEAR16 回應建立 header，然後更新範例，以提供能產生可播放音訊的指引。確認對於除錯串流合成的使用者而言，產生輸出的處理方式是清楚的。

由索引模型根據 Issue 內容生成。