### Issue # (if applicable) Closes #34743 ### Reason for this change Database insights for Aurora Cluster was previously implemented in #32851. Database insights is also supported for RDS instances, but the current L2 construct does not support it. https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/Database-Insights.html ### Description of changes - Add databaseInsightsMode property to DatabaseInstance class - Consolidate validation logic by creating a shared validation module that works for both cluster and instance types ### Describe any new or updated permissions being added N/A ### Description of how you validated changes Add unit tests and integ tests. ### Checklist - [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md) ---- *By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*