chore(ec2): add m8i, m8i-flex, r8i, r8i-flex instance class (aws#35364)

### Issue # (if applicable)
None

### Reason for this change
https://aws.amazon.com/about-aws/whats-new/2025/08/amazon-ec2-m8i-and-m8i-flex-instances-generally-available/
https://aws.amazon.com/about-aws/whats-new/2025/08/memory-optimized-amazon-ec2-r8i-r8i-flex-instances/

### Description of changes
Add m8i, m8i-flex, r8i, r8i-flex instance class

### Description of how you validated changes
```console
$ aws ec2 describe-instance-types | grep -e m8i -e r8i
            "InstanceType": "r8i.48xlarge",
            "InstanceType": "r8i-flex.8xlarge",
            "InstanceType": "m8i.16xlarge",
            "InstanceType": "m8i-flex.2xlarge",
```

### 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: phuhung273

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

@@ -440,6 +440,28 @@ export enum InstanceClass {
    */
   R7IZ = 'r7iz',
 
+  /**
+   * Memory optimized instances based on custom Intel Xeon Scalable 6 processors, available only on AWS
+   */
+  MEMORY8_INTEL_BASE = 'memory8-intel-base',
+
+  /**
+   * Memory optimized instances based on custom Intel Xeon Scalable 6 processors, available only on AWS
+   */
+  R8I = 'r8i',
+
+  /**
+   * Memory optimized flexible instances based on custom Intel Xeon Scalable 6 processors, available only on AWS
+   * Provide up to 20% higher performance, 2.5x more memory throughput, and can scale up to full CPU performance 95% of the time
+   */
+  MEMORY8_INTEL_FLEX = 'memory8-intel-flex',
+
+  /**
+   * Memory optimized flexible instances based on custom Intel Xeon Scalable 6 processors, available only on AWS
+   * Provide up to 20% higher performance, 2.5x more memory throughput, and can scale up to full CPU performance 95% of the time
+   */
+  R8I_FLEX = 'r8i-flex',
+
   /**
    * Memory optimized instances based on 4th generation AMD EPYC (codename Genoa), 7th generation
    */
@@ -1339,6 +1361,28 @@ export enum InstanceClass {
    */
   M8GD = 'm8gd',
 
+  /**
+   * Standard instances based on custom Intel Xeon Scalable 6 processors, available only on AWS
+   */
+  STANDARD8_INTEL = 'standard8-intel',
+
+  /**
+   * Standard instances based on custom Intel Xeon Scalable 6 processors, available only on AWS
+   */
+  M8I = 'm8i',
+
+  /**
+   * Flexible instances based on custom Intel Xeon Scalable 6 processors, available only on AWS
+   * Provide up to 20% higher performance, 2.5x more memory throughput, and can scale up to full CPU performance 95% of the time
+   */
+  STANDARD8_INTEL_FLEX = 'standard8-intel-flex',
+
+  /**
+   * Flexible instances based on custom Intel Xeon Scalable 6 processors, available only on AWS
+   * Provide up to 20% higher performance, 2.5x more memory throughput, and can scale up to full CPU performance 95% of the time
+   */
+  M8I_FLEX = 'm8i-flex',
+
   /**
    * Standard instances with high memory and compute capacity based on Intel Xeon Scalable (Sapphire Rapids) processors, 7th generation
    */
@@ -1795,6 +1839,10 @@ export class InstanceType {
       [InstanceClass.R8G]: 'r8g',
       [InstanceClass.MEMORY8_GRAVITON4_NVME_DRIVE]: 'r8gd',
       [InstanceClass.R8GD]: 'r8gd',
+      [InstanceClass.MEMORY8_INTEL_BASE]: 'r8i',
+      [InstanceClass.R8I]: 'r8i',
+      [InstanceClass.MEMORY8_INTEL_FLEX]: 'r8i-flex',
+      [InstanceClass.R8I_FLEX]: 'r8i-flex',
       [InstanceClass.COMPUTE3]: 'c3',
       [InstanceClass.C3]: 'c3',
       [InstanceClass.COMPUTE4]: 'c4',
@@ -1955,6 +2003,10 @@ export class InstanceType {
       [InstanceClass.M7I]: 'm7i',
       [InstanceClass.STANDARD7_INTEL_FLEX]: 'm7i-flex',
       [InstanceClass.M7I_FLEX]: 'm7i-flex',
+      [InstanceClass.STANDARD8_INTEL]: 'm8i',
+      [InstanceClass.M8I]: 'm8i',
+      [InstanceClass.STANDARD8_INTEL_FLEX]: 'm8i-flex',
+      [InstanceClass.M8I_FLEX]: 'm8i-flex',
       [InstanceClass.STANDARD7_AMD]: 'm7a',
       [InstanceClass.M7A]: 'm7a',
       [InstanceClass.HIGH_COMPUTE_MEMORY1]: 'z1d',