chore(eks-v2-alpha): backfill missing enums for eks-v2-alpha (#33630)

### Description of changes

backfill missing enums for eks-v2-alpha

### 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*

Author: paulhcsun

packages/@aws-cdk/aws-eks-v2-alpha/lib/managed-nodegroup.ts

@@ -103,6 +103,10 @@ export enum CapacityType {
    * on-demand instances
    */
   ON_DEMAND = 'ON_DEMAND',
+  /**
+   * capacity block instances
+   */
+  CAPACITY_BLOCK = 'CAPACITY_BLOCK',
 }
 
 /**