first pass at turn based conversation

vocode/streaming/models/message.py

@@ -0,0 +1,16 @@
+from enum import Enum
+from .model import TypedModel
+from enum import Enum
+
+
+class MessageType(str, Enum):
+    BASE = "message_base"
+    SSML = "message_ssml"
+
+
+class BaseMessage(TypedModel, type=MessageType.BASE):
+    text: str
+
+
+class SSMLMessage(BaseMessage, type=MessageType.SSML):
+    ssml: str