AWS::RedshiftServerless::Namespace - Support for SecretARN return value when "ManageAdminPassword" is set as true

### Name of the resource

AWS::RedshiftServerless::Namespace

### Resource name

_No response_

### Description

When we create RedshiftServerless Namespace having ["ManageAdminPassword" property](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-redshiftserverless-namespace.html#cfn-redshiftserverless-namespace-manageadminpassword) as true, in the backend it creates a Secrets Manager's secret to store the credentials. I want that secret's ARN value in the ["Return values"](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-redshiftserverless-namespace.html#aws-resource-redshiftserverless-namespace-return-values) of the resource type "[AWS::RedshiftServerless::Namespace](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-redshiftserverless-namespace.html)".

I can understand that there is a separate API call of "CreateSecret" that happens in this process and secret's ARN is not a specific property of Redshift Serverless Namespace. Hence, I am creating this as a feature request if it can be supported.

### Other Details

_No response_