add new fields for struct of webhook sent response

v1/types.go

@@ -432,6 +432,8 @@ type WebhookMessageSentResponse struct {
 	ExternalMessageID  string            `json:"external_message_id"`
 	Error              *MessageSentError `json:"error,omitempty"`
 	Async              bool              `json:"async"`
+	ExternalCustomerID string            `json:"external_customer_id,omitempty"`
+	ExternalChatID     string            `json:"external_chat_id,omitempty"`
 }
 
 // MessageSentError type.