processors(realtime-ai): add support for appending to the LLM context

src/pipecat/frames/frames.py

@@ -158,6 +158,15 @@ class LLMMessagesFrame(DataFrame):
     messages: List[dict]
 
 
+@dataclass
+class LLMMessagesAppendFrame(DataFrame):
+    """A frame containing a list of LLM messages that neeed to be added to the
+    current context.
+
+    """
+    messages: List[dict]
+
+
 @dataclass
 class LLMMessagesUpdateFrame(DataFrame):
     """A frame containing a list of new LLM messages. These messages will