Webhook订阅端点 union
传递webhook的端点。可选的类型
[WebhookEventBridgeEndpoint](https://shopify.dev/docs/admin-api/graphql/reference/events/webhookeventbridgeendpoint)
[WebhookHttpEndpoint](https://shopify.dev/docs/admin-api/graphql/reference/events/webhookhttpendpoint)