Updated warning message about missing function in template (#5347)

Co-authored-by: Wing Fung Lau <4760060+hawflau@users.noreply.github.com>

samcli/local/apigw/local_apigw_service.py

@@ -686,7 +686,7 @@ def _request_handler(self, **kwargs):
 
             LOG.warning(
                 "Failed to find a Function to invoke a Lambda authorizer, verify that "
-                "this Function exists locally if it is not a remote resource."
+                "this Function is defined and exists locally in the template."
             )
         except Exception as ex:
             # re-raise the catch all exception after we track it in our telemetry