feat(rds): add ability to specify PreferredMaintenanceWindow to RDS c…

…luster database instances (#29033)

### Issue # (if applicable)

Closes [#16954](#16954)

### Reason for this change
Noticed that we were able to specify preferredMaintenanceWindow for a cluster, but unable to do so for the instances created under the cluster. Instead, AWS (semi-)randomly assigns a maintenance window ([doc](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_UpgradeDBInstance.Maintenance.html#Concepts.DBMaintenance)) for the instances, which leads to things being out of sync b/w the cluster and its child instances

There are some workarounds as mentioned in the issue above, but those are a little hacky (imo) and I figured adding the preferredMaintenanceWindow as an instance prop is a better long-term solution. Also, it might be hard for other developers to find the workarounds as they are only mentioned in the above issue and aren't available through normal channels (Stack overflow/official CDK docs) 

### Description of changes
Added optional preferredMaintenanceWindow field under `InstanceProps`, and passed that field in during the creation of the `CfnDBInstance`. Also added a quick unit test

### Description of how you validated changes
Added a unit test, did not add integ tests. Ran `yarn build` and `yarn test`

Callout: I was unable to run integration tests locally, kept getting errors with `yarn integ --directory packages/aws-cdk-lib/aws-rds` and `yarn integ-runner --directory packages/aws-cdk-lib/aws-rds` - `Error: Cannot find module './integ-runner.js'`, not sure if I'm missing something

### 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)

No breaking changes

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk-lib/aws-rds/README.md

@@ -1204,3 +1204,23 @@ The `vpc` parameter is optional.
 If not provided, the cluster will be created in the default VPC of the account and region.
 As this VPC is not deployed with AWS CDK, you can't configure the `vpcSubnets`, `subnetGroup` or `securityGroups` of the Aurora Serverless Cluster.
 If you want to provide one of `vpcSubnets`, `subnetGroup` or `securityGroups` parameter, please provide a `vpc`.
+
+### Preferred Maintenance Window
+
+When creating an RDS cluster, it is possible to (optionally) specify a preferred maintenance window for the cluster as well as the instances under the cluster.
+See [AWS docs](https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/USER_UpgradeDBInstance.Maintenance.html#Concepts.DBMaintenance) for more information regarding maintenance windows.
+
+The following code snippet shows an example of setting the cluster's maintenance window to 22:15-22:45 (UTC) on Saturdays, but setting the instances' maintenance window
+to 23:15-23:45 on Sundays
+
+```ts
+declare const vpc: ec2.Vpc;
+new rds.DatabaseCluster(this, 'DatabaseCluster', {
+  engine: rds.DatabaseClusterEngine.AURORA,
+  instanceProps: {
+    vpc: vpc,
+    preferredMaintenanceWindow: 'Sun:23:15-Sun:23:45',
+  },
+  preferredMaintenanceWindow: 'Sat:22:15-Sat:22:45',
+});
+```

packages/aws-cdk-lib/aws-rds/lib/cluster.ts

@@ -1415,6 +1415,7 @@ function legacyCreateInstances(cluster: DatabaseClusterNew, props: DatabaseClust
       autoMinorVersionUpgrade: instanceProps.autoMinorVersionUpgrade,
       allowMajorVersionUpgrade: instanceProps.allowMajorVersionUpgrade,
       deleteAutomatedBackups: instanceProps.deleteAutomatedBackups,
+      preferredMaintenanceWindow: instanceProps.preferredMaintenanceWindow,
     });
 
     // For instances that are part of a cluster:

packages/aws-cdk-lib/aws-rds/lib/props.ts

@@ -101,6 +101,17 @@ export interface InstanceProps {
    * @default - `true` if `vpcSubnets` is `subnetType: SubnetType.PUBLIC`, `false` otherwise
    */
   readonly publiclyAccessible?: boolean;
+
+  /**
+   * A preferred maintenance window day/time range. Should be specified as a range ddd:hh24:mi-ddd:hh24:mi (24H Clock UTC).
+   *
+   * Example: 'Sun:23:45-Mon:00:15'
+   *
+   * @default - 30-minute window selected at random from an 8-hour block of time for
+   * each AWS Region, occurring on a random day of the week.
+   * @see https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/USER_UpgradeDBInstance.Maintenance.html#Concepts.DBMaintenance
+   */
+  readonly preferredMaintenanceWindow?: string;
 }
 
 /**

packages/aws-cdk-lib/aws-rds/test/cluster.test.ts

@@ -209,6 +209,30 @@ describe('cluster new api', () => {
         ],
       });
     });
+
+    test('preferredMaintenanceWindow provided in InstanceProps', () => {
+      // GIVEN
+      const stack = testStack();
+      const vpc = new ec2.Vpc(stack, 'VPC');
+
+      const PREFERRED_MAINTENANCE_WINDOW: string = 'Sun:12:00-Sun:13:00';
+
+      // WHEN
+      new DatabaseCluster(stack, 'Database', {
+        engine: DatabaseClusterEngine.AURORA,
+        instanceProps: {
+          vpc: vpc,
+          preferredMaintenanceWindow: PREFERRED_MAINTENANCE_WINDOW,
+        },
+      });
+
+      // THEN
+      const template = Template.fromStack(stack);
+      // maintenance window is set
+      template.hasResourceProperties('AWS::RDS::DBInstance', Match.objectLike({
+        PreferredMaintenanceWindow: PREFERRED_MAINTENANCE_WINDOW,
+      }));
+    });
   });
 
   describe('migrate from instanceProps', () => {