Cloudformation support Read replicate promotion to master

### Name of the resource

Other

### Resource name

AWS::RDS::DBInstance

### Description

Would like the ability to add a flag or some other reference for an RDS Read Replica to automatically promote the replica to a primary DB in an update where the primary is removed from the stack.

### Other Details

_No response_

Start by reviewing the AWS::RDS::DBInstance resource behavior for read replicas and stack updates that remove the primary. Compare that behavior with the requested automatic promotion flow. Done means CloudFormation supports a clear flag or reference that promotes the replica when its primary is removed from the stack.

Written by the indexing model from the issue text.