docs(triggers): add consideration about invocationType for the behavior of trigger failures (#26450)

TriggerCustomResourceProvider takes only the status code of Invoke API call into account.
https://github.com/aws/aws-cdk/blob/7a6f953fe5a4d7e0ba5833f06596b132c95e0709/packages/aws-cdk-lib/triggers/lib/lambda/index.ts#L69-L73

If invocationType is `EVENT`, Lambda function is invoked asynchronously. In that case, if Lambda function is invoked successfully, the trigger will success regardless of the result for the function execution. I add this consideration into README.

Closes #26341

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Author: tam0ri

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

@@ -57,6 +57,9 @@ deployment will fail, as if a resource failed to provision. This makes it easy
 to implement "self tests" via triggers by simply making a set of assertions on
 some provisioned infrastructure.
 
+Note that this behavior is only applied when invocationType is `REQUEST_RESPONSE`. When invocationType is `EVENT`, Lambda function is invoked asynchronously.
+In that case, if Lambda function is invoked successfully, the trigger will success regardless of the result for the function execution.
+
 ## Order of Execution
 
 By default, a trigger will be executed by CloudFormation after the associated