Adding UtteranceEnd support for Deepgram

[hackyon]

Adding support for UtteranceEnd to Deepgram agent plugin. The UtteranceEnd is another feature offered by Deepgram to detect end of speech.

The Deepgram documentation is here:
https://developers.deepgram.com/docs/utterance-end

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Latest commit: 90ab6cd

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[theomonnom]

Hey, can you default it to None?

[theomonnom]

Is it being sent every time we finish speaking? If so, we should remove the previous dispatch of END_OF_SPEECH to avoid duplicate events, (only when end_of_utterance_ms is enabled)