docs(apigateway): add warning about split stack technique (#29691)

### Issue #29690

Closes #29690

### Reason for this change

Regarding the stack separation of RestApi and Resource, there is no documentation about the fact that Deployment is not automatically created. When I actually add resources to the code documented and try cdk deploy for the second time and beyond, a new deployment is not created, and the latest resources are not reflected.

### Description of changes

I added a note and related links to the documentation.

### Description of how you validated changes

Nothing. It is just to change the description.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk-lib/aws-apigateway/README.md

@@ -267,6 +267,11 @@ The following example uses sets up two Resources '/pets' and '/books' in separat
 
 [Resources grouped into nested stacks](test/integ.restapi-import.lit.ts)
 
+> **Warning:** In the code above, an API Gateway deployment is created during the initial CDK deployment.
+However, if there are changes to the resources in subsequent CDK deployments, a new API Gateway deployment is not
+automatically created. As a result, the latest state of the resources is not reflected. To ensure the latest state
+of the resources is reflected, a manual deployment of the API Gateway is required after the CDK deployment.
+
 ## Integration Targets
 
 Methods are associated with backend integrations, which are invoked when this