AWS::CloudFormation::StackSet - return instance Outputs

### Name of the resource

AWS::CloudFormation::StackSet

### Resource name

_No response_

### Description

It would be a great help for the AWS community using CloudFormation templates for IaC to have [AWS::CloudFormation::StackSet](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-cloudformation-stackset.html) returning [not just its logical ID](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-cloudformation-stackset.html#aws-resource-cloudformation-stackset-return-values), but also be **able to return its instance Outputs**.

Usage template sample:

```yaml
WAFStackSet:
Type: AWS::CloudFormation::StackSet
Properties:
StackSetName: WAFStackSet
Description: CloudFormation StackSet used to provision WAF resources
PermissionModel: SELF_MANAGED
StackInstancesGroup:
- DeploymentTargets:
Accounts: [!Ref "AWS::AccountId"]
Regions: [us-east-1]
TemplateBody: |
AWSTemplateFormatVersion: 2010-09-09
Description: WAF Stack
Resources:
WebACL:
Type: AWS::WAFv2::WebACL
Properties:
...
Outputs:
WAFWebACLId:
Value: !GetAtt WebACL.Id

CloudFrontDistribution:
Type: AWS::CloudFront::Distribution
Properties:
DistributionConfig:
WebACLId: !GetAtt WAFStackSet.Outputs.WAFWebACLId
...

```

With this improvement being a solution to overcome limitations like:
* #523
* #546

Because there are also missing:
* #562
* #630

Additional references from re:Post that would benefit with this:
* [How to access StackSet instances outputs | AWS re:Post](https://repost.aws/questions/QUSAhSA2u6TraXHxzAH6GzLg/how-to-access-stackset-instances-outputs)
* [Reference cross-instance StackSet outputs | AWS re:Post](https://repost.aws/questions/QU52Z-JTP4QJq5zJstxwVA5g/reference-cross-instance-stackset-outputs)

### Other Details

_No response_

No repository files or tests are named. Start by reading the AWS::CloudFormation::StackSet return-values documentation and the linked issues and re:Post references; done means a StackSet instance output can be referenced as shown in the sample.

Written by the indexing model from the issue text.