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]))
```

Start with texttospeech/snippets/streaming_tts_quickstart.py around lines 46-48 and review the linked WAV specification. Determine how the header should be created for the headerless 24,000 Hz LINEAR16 responses, then update the sample to provide guidance that produces playable audio. Confirm the resulting output handling is clear to users debugging streaming synthesis.

Escrita pelo modelo de indexação a partir do texto da issue.