(rds): Support cross-region automated backups

### Describe the feature

RDS allows to enable cross-region automated backups quite easily ([see docs](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_ReplicateBackups.html#AutomatedBackups.Replicating.Enable)) by choosing:
- the destination region
- the replicated backup retention period
- the KMS key

### Use Case

It is currently not possible to do the same with only the CDK RDS module.
I assume it would be possible to mimic this behavior with a Lambda, but this requires high amounts of work, and does not seem to be documented anywhere.

### 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

2.32.1

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

N/A

Start by reading the AWS RDS cross-region automated backups documentation linked in the issue and then locate the CDK RDS module responsible for backup configuration. Done means the module can configure a destination region, replicated backup retention period, and KMS key without requiring a separate Lambda.

Written by the indexing model from the issue text.