Refactor grpc-balancer to use Gunicorn and update playbook.yml for deployment

- Replaced the SSL server implementation in grpc-balancer.py with Gunicorn for improved performance and scalability.
- Updated playbook.yml to use Gunicorn for starting the grpc-balancer service, including SSL certificate configuration.
- Removed the waitress dependency in favor of Gunicorn, streamlining the application setup.

grpc-balancer.py

@@ -318,11 +318,4 @@ if __name__ == '__main__':
     upload_thread = threading.Thread(target=upload_stats_to_grist, daemon=True, args=(grist_callback,))
     upload_thread.start()
 
-    from waitress import serve
-    import ssl
-    
-    ssl_context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
-    ssl_context.load_cert_chain('/root/node/cert.pem', '/root/node/key.pem')
-    
-    logging.info(f"Starting SSL server on port {PORT}")
-    serve(app, host='0.0.0.0', port=PORT, threads=MAX_WORKERS, connection_limit=1000, _ssl_context=ssl_context)
+    app.run(host='0.0.0.0', port=PORT)