Deprecate event namespace config knob (#2218)

reflex/config.py

@@ -286,6 +286,12 @@ class Config(Base):
             The namespace for websocket.
         """
         if self.event_namespace:
+            console.deprecate(
+                feature_name="Passing event_namespace in the config",
+                reason="",
+                deprecation_version="0.3.5",
+                removal_version="0.3.10",
+            )
             return f'/{self.event_namespace.strip("/")}'
 
         event_url = constants.Endpoint.EVENT.get_url()