[Resource Type] - [Enhancement] - AWS::RDS::GlobalCluster GlobalEndpoint attribute

### Name of the resource

AWS::RDS::GlobalCluster

### Description

Currently the global writer endpoint is not exposed as an attribute (screenshot of docs below). It would be beneficial to have this available as an output instead of needing to write a custom resource to fetch it so that it can be used in other resources.

It appears to be defined in the [resource specification](https://d1uauaxba7bl26.cloudfront.net/latest/gzip/CloudFormationResourceSpecification.json) but not available for use.
```
"Attributes": {
"GlobalEndpoint.Address": {
"PrimitiveType": "String"
},
"GlobalEndpoint": {
"Type": "GlobalEndpoint"
}
}
```

## Docs
https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-resource-rds-globalcluster.html#aws-resource-rds-globalcluster-return-values

## Example CFN
```
{
"GlobalCluster": {
"Type": "AWS::RDS::GlobalCluster",
"Properties": {
"DeletionProtection": false,
"Engine": "aurora-postgresql",
"EngineVersion": "15.12",
"GlobalClusterIdentifier": "ken-test",
"StorageEncrypted": true
}
},
"TestAttrGlobalEndpointFE635CBC": {
"Type": "AWS::SSM::Parameter",
"Properties": {
"Name": "testing-endpoint",
"Type": "String",
"Value": {
"Fn::GetAtt": ["GlobalCluster", "GlobalEndpoint"]
}
}
}
}
```

However, I get this output
```
CREATE_FAILED | AWS::SSM::Parameter | TestAttrGlobalEndpointFE635CBC
Attribute 'GlobalEndpoint' does not exist
```

Also related - https://github.com/aws/aws-cdk/issues/33808

Start by comparing the AWS::RDS::GlobalCluster resource specification entry with the CloudFormation return-values documentation. Reproduce the provided Fn::GetAtt example and verify whether GlobalEndpoint and GlobalEndpoint.Address are exposed. Done means the attribute can be used as an output by other resources and the documentation reflects the supported return value.

Written by the indexing model from the issue text.