feat(ec2): add d3 and d3en instances (#17782)

`d3` and `d3en` storage optimized instances:
https://aws.amazon.com/blogs/aws/ec2-update-d3-d3en-dense-storage-instances/

![image](https://user-images.githubusercontent.com/31543/144115255-be750884-a00b-4bda-98bb-0addbbe15b77.png)

![image](https://user-images.githubusercontent.com/31543/144115270-a5e75a1d-b7aa-483f-adcf-b50562aab6d5.png)

CFN docs have already been updated:
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-instance.html#cfn-ec2-instance-instancetype

----

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

Author: robertd

packages/@aws-cdk/aws-ec2/lib/instance-types.ts

@@ -392,6 +392,26 @@ export enum InstanceClass {
    */
   D2 = 'd2',
 
+  /**
+   * Storage-optimized instances, 3rd generation
+   */
+  STORAGE3 = 'd3',
+
+  /**
+   * Storage-optimized instances, 3rd generation
+   */
+  D3 = 'd3',
+
+  /**
+  * Storage-optimized instances, 3rd generation
+  */
+  STORAGE3_ENHANCED_NETWORK = 'd3en',
+
+  /**
+  * Storage-optimized instances, 3rd generation
+  */
+  D3EN = 'd3en',
+
   /**
    * Storage/compute balanced instances, 1st generation
    */