feat(redshift): add missing current generation RA3 NodeTypes (#12784)

Adds the missing Redshift RA3 NodeTypes (ra3.xlplus, ra3.4xlarge).

closes #12783


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

Author: mbeacom

packages/@aws-cdk/aws-redshift/lib/cluster.ts

@@ -40,6 +40,14 @@ export enum NodeType {
    * dc2.8xlarge
    */
   DC2_8XLARGE = 'dc2.8xlarge',
+  /**
+   * ra3.xlplus
+   */
+  RA3_XLPLUS = 'ra3.xlplus',
+  /**
+   * ra3.4xlarge
+   */
+  RA3_4XLARGE = 'ra3.4xlarge',
   /**
    * ra3.16xlarge
    */