add twilio-chatbot example with README.md info how to start app

created twilio_websocket_service.py, TwilioFrameSerializer.py

moved pcm_16000_to_ulaw_8000 and ulaw_8000_to_pcm_16000 to src/pipecat/utils/audio.py
fixed callback on disconnect

examples/twilio-chatbot/server.py

@@ -0,0 +1,32 @@
+from fastapi import FastAPI, WebSocket, WebSocketDisconnect
+from fastapi.middleware.cors import CORSMiddleware
+import uvicorn
+from starlette.responses import HTMLResponse
+from test_bot import run_bot
+
+app = FastAPI()
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],  # Allow all origins for testing
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+
+@app.post('/start_call')
+async def start_call():
+    print("POST TwiML")
+    return HTMLResponse(content=open("templates/streams.xml").read(), media_type="application/xml")
+
+
+@app.websocket("/ws")
+async def websocket_endpoint(websocket: WebSocket):
+    await websocket.accept()
+    print("WebSocket connection accepted")
+    await run_bot(websocket)
+
+
+if __name__ == "__main__":
+    uvicorn.run(app, host="0.0.0.0", port=8765)