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/Dockerfile

@@ -0,0 +1,20 @@
+# Use an official Python runtime as a parent image
+FROM python:3.10-bullseye
+
+# Set the working directory in the container
+WORKDIR /twilio-chatbot
+
+# Copy the requirements file into the container
+COPY requirements.txt .
+
+# Install any needed packages specified in requirements.txt
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy the current directory contents into the container
+COPY . .
+
+# Expose the desired port
+EXPOSE 8765
+
+# Run the application
+CMD ["uvicorn", "server:app", "--host", "0.0.0.0", "--port", "8765"]