feat: Add new sample for response streaming

[janell-chen]

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[snippet-bot]

Here is the summary of changes.

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• functions/responsestreaming/StreamBigQuery/Function.cs:15, tag functions_response_streaming

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[jskeet]

(Sorry for so many extra comments... with the solution in place, it was much easier for me to pull, review locally, test it myself etc.)

[janell-chen]

Thanks @jskeet, just resolved all the comments. Let me know how this looks

[jskeet]

One final nit to address, and then @amanda-tarafa and I can squash and merge (to avoid the merge commits).

[janell-chen]

@jskeet done, thank you!