Use "developer" role for programmatic conversation-kickoff messages

These messages are developer instructions to the assistant (e.g. "Please
introduce yourself to the user"), not simulated user input. The
"developer" role is semantically correct for this purpose.

examples/foundational/55d-update-settings-assemblyai-stt.py

@@ -104,7 +104,9 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
         logger.info(
             "Phase 1: No keyterms boosting - try saying 'Xiomara', 'Saoirse', or 'Krzystof'"
         )
-        context.add_message({"role": "user", "content": "Please introduce yourself to the user."})
+        context.add_message(
+            {"role": "developer", "content": "Please introduce yourself to the user."}
+        )
         await task.queue_frames([LLMRunFrame()])
 
         await asyncio.sleep(15)