aws-rds: Global database support for write forwarding?

### Describe the feature

As of this issue, write forwarding is supported for MySQL Aurora global databases, but not for postgres. I think this feature is incredibly important for multi-region rds, as it simplifies the workflow immensely. As of a month ago there is [support for active-active postgresql multi region using postgres extensions](https://aws.amazon.com/blogs/database/using-pgactive-active-active-replication-extension-for-postgresql-on-amazon-rds-for-postgresql/), and I was curious if there's a roadmap for this support natively through cdk

### Use Case

Used to incredibly simplify architecture management on the dev side. It would make multi region rds way more usable.

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

latest

### Environment details (OS name and version, etc.)

Mac OS ventura 13.6

No file, test, or implementation entry point is named. Start by reviewing the AWS CDK RDS support and AWS documentation for PostgreSQL global databases and write forwarding, then determine whether the capability is available through the underlying service. Done would require an agreed API and a defined implementation and test scope.

Written by the indexing model from the issue text.