feat(ec2): add g6 instance (#30693)

### Issue # (if applicable)

Closes #30683 

### Reason for this change

G6 instances are not yet supported by CDK L2

### Description of changes

Added G6 instance class

### Description of how you validated changes

Added `g6` to existing unit test

### 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: mellevanderlinde

Diff for: packages/aws-cdk-lib/aws-ec2/lib/instance-types.ts

@@ -890,6 +890,16 @@ export enum InstanceClass {
    */
   G5G = 'g5g',
 
+  /**
+   * Graphics-optimized instances, 6th generation
+   */
+  GRAPHICS6 = 'graphics6',
+
+  /**
+   * Graphics-optimized instances, 6th generation
+   */
+  G6 = 'g6',
+
   /**
    * Parallel-processing optimized instances, 2nd generation
    */
@@ -1568,6 +1578,8 @@ export class InstanceType {
       [InstanceClass.G5]: 'g5',
       [InstanceClass.GRAPHICS5_GRAVITON2]: 'g5g',
       [InstanceClass.G5G]: 'g5g',
+      [InstanceClass.GRAPHICS6]: 'g6',
+      [InstanceClass.G6]: 'g6',
       [InstanceClass.PARALLEL2]: 'p2',
       [InstanceClass.P2]: 'p2',
       [InstanceClass.PARALLEL3]: 'p3',

Diff for: packages/aws-cdk-lib/aws-ec2/test/instance.test.ts

@@ -126,7 +126,7 @@ describe('instance', () => {
   });
   test('instance architecture is correctly discerned for x86-64 instance', () => {
     // GIVEN
-    const sampleInstanceClasses = ['c5', 'm5ad', 'r5n', 'm6', 't3a', 'r6i', 'r6a', 'p4de', 'p5', 'm7i-flex']; // A sample of x86-64 instance classes
+    const sampleInstanceClasses = ['c5', 'm5ad', 'r5n', 'm6', 't3a', 'r6i', 'r6a', 'g6', 'p4de', 'p5', 'm7i-flex']; // A sample of x86-64 instance classes
 
     for (const instanceClass of sampleInstanceClasses) {
       // WHEN