Support max_characters for text to speech models/drivers

[vachillo]

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Is your feature request related to a problem? Please describe.
OpenAI's tts-1 model has an input character limit of 4096. The driver should be updated to split up API calls with this max limit in mind.

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[collindutter]

I'm not sure this necessarily needs to live in the framework. We don't really prevent max input size for basic Driver interactions. We could put this logic in an Engine, but that feels overkill. In the case of the PromptSummaryEngine there is some complexity in summarizing as much text as possible while maintaining a running summary. But I don't think the same complexity exists for this use-case.

Pulling a snippet you've shared:

        prompt_str = self.prompt_joiner.join(prompts).strip()
        new_prompts = [
            prompt_str[i : i + self.text_to_speech_driver.max_characters]
            for i in range(0, len(prompt_str), self.text_to_speech_driver.max_characters)
        ]
        return [self.text_to_speech_driver.try_text_to_audio(prompt=prompt) for prompt in new_prompts]