Introduced LLMTextProcessor and deprecatd custom text_aggregators in TTS

Introduced `LLMTextProcessor`: A new processor meant to allow customization for how
LLMTextFrames should be aggregated and considered. It's purpose is to turn
`LLMTextFrame`s into `AggregatedTextFrame`s. By default, a TTSService will still
aggregate `LLMTextFrame`s by sentence for the service to consume. However, if you
wish to override how the llm text is aggregated, you should no longer override the
TTS's internal text_aggregator, but instead, insert this processor between your LLM
and TTS in the pipeline.

tests/test_piper_tts.py

@@ -13,6 +13,7 @@ import pytest
 from aiohttp import web
 
 from pipecat.frames.frames import (
+    AggregatedTextFrame,
     ErrorFrame,
     TTSAudioRawFrame,
     TTSSpeakFrame,
@@ -74,6 +75,7 @@ async def test_run_piper_tts_success(aiohttp_client):
         ]
 
         expected_returned_frames = [
+            AggregatedTextFrame,
             TTSStartedFrame,
             TTSAudioRawFrame,
             TTSAudioRawFrame,
@@ -121,7 +123,7 @@ async def test_run_piper_tts_error(aiohttp_client):
             TTSSpeakFrame(text="Error case."),
         ]
 
-        expected_down_frames = [TTSStoppedFrame, TTSTextFrame]
+        expected_down_frames = [AggregatedTextFrame, TTSStoppedFrame, TTSTextFrame]
 
         expected_up_frames = [ErrorFrame]