feat(ec2): add m5zn instances (#17757)

`m5zn` instances release notes:
https://aws.amazon.com/blogs/aws/new-ec2-m5zn-instances-fastest-intel-xeon-scalable-cpu-in-the-cloud/

Docs have already been updated a while ago:
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

@@ -88,6 +88,16 @@ export enum InstanceClass {
    */
   M5DN = 'm5dn',
 
+  /**
+   * Standard instances with high memory and compute capacity based on Intel Xeon Scalable (Cascade Lake) processors, 5nd generation
+   */
+  STANDARD5_HIGH_COMPUTE = 'm5zn',
+
+  /**
+   * Standard instances with high memory and compute capacity based on Intel Xeon Scalable (Cascade Lake) processors, 5nd generation
+   */
+  M5ZN = 'm5zn',
+
   /**
    * Memory optimized instances, 3rd generation
    */