[AWS::Organizations::MultiPartyApproval] - [Feature Request] - adding the support for "AWS Multi-party Approval" via Cloudformation.

### Name of the resource

Other

### Resource name

AWS::Organizations::MultiPartyApproval

### Description

See https://aws.amazon.com/blogs/aws/aws-backup-adds-new-multi-party-approval-for-logically-air-gapped-vaults/

https://docs.aws.amazon.com/mpa/latest/userguide/what-is.html

It would be great to be able to deploy this using IaC

### Other Details

_No response_

Start with the AWS Multi-party Approval announcement and user guide linked in the issue, then review how this repository records coverage requests for new CloudFormation resources. No repository files, entry points, or tests are named, so first identify the expected resource schema and applicable coverage workflow. Done means the requested AWS::Organizations::MultiPartyApproval support is fully specified for CloudFormation.

Written by the indexing model from the issue text.