[AWS::SecretsManager::SecretTargetAttachment] - [Coverage] - Target Attachment missing support for Redshift Serverless Namespace

### Name of the resource

AWS::SecretsManager::SecretTargetAttachment

### Resource name

_No response_

### Description

Currently, there is support the following resources:
- AWS::RDS::DBInstance
- AWS::RDS::DBCluster
- AWS::Redshift::Cluster
- AWS::DocDB::DBInstance
- AWS::DocDB::DBCluster

However, there is no support for the Redshift Namespace type (AWS::RedshiftServerless::Namespace). This is creating issues as we cannot properly make use of CloudFormation. We could make use of the secrets manager resources directly, but it would be better to have this functionality in place.

### Other Details

_No response_

Start by reviewing the existing coverage for AWS::SecretsManager::SecretTargetAttachment and its listed RDS, Redshift, and DocDB target resources. Compare that behavior with AWS::RedshiftServerless::Namespace and identify the project entry point and validation coverage; done means the namespace target is supported for CloudFormation use. No files or tests are named in the issue.

Written by the indexing model from the issue text.