Pulumi Policy Pack should consider _both_ RDS clusters and instances in rules

[psirenny]

AWS native (and perhaps classic?) doesn’t allow setting the same properties on an instance and a cluster. For example, enabling encryption on the cluster and its instance results in an error. This makes sense; otherwise, instance settings could conflict with their owning cluster. In some cases, settings must be applied only to the cluster or the instance based on the type of RDS deployment.

However… The default RDS cluster and RDS instance policy pack rules don’t consider this. They dictate that specific settings — such as enabling encryption — must be applied to both resources. A rule that’s impossible to comply with. An ideal rule would look at both the RDS cluster and its instances to see if they're passing/failing compliance.