fix(opensearchservice): add i8g nodes validation without EBS (#35668)

### Issue # (if applicable)

Closes #35666.

### Reason for this change
Cannot create i8g data nodes without EBS due to validation logic.


### Description of changes
Enable create i8g data nodes by adding i8g type to `unSupportEbsInstanceType` .


### Describe any new or updated permissions being added
N/A



### Description of how you validated changes
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: mazyu36

packages/aws-cdk-lib/aws-opensearchservice/lib/domain.ts

@@ -1649,6 +1649,7 @@ export class Domain extends DomainBase implements IDomain, ec2.IConnectable {
       ec2.InstanceClass.R6GD,
       ec2.InstanceClass.I4G,
       ec2.InstanceClass.I4I,
+      ec2.InstanceClass.I8G,
       ec2.InstanceClass.IM4GN,
       ec2.InstanceClass.R7GD,
     ];

packages/aws-cdk-lib/aws-opensearchservice/test/domain.test.ts

@@ -2006,6 +2006,7 @@ each(testedOpenSearchVersions).describe('custom error responses', (engineVersion
     'im4gn.2xlarge.search',
     'i4g.large.search',
     'i4i.xlarge.search',
+    'i8g.4xlarge.search',
     'r7gd.xlarge.search',
   ])('error when %s instance type is specified with EBS enabled', (dataNodeInstanceType) => {
     expect(() => new Domain(stack, 'Domain2', {
@@ -2017,7 +2018,25 @@ each(testedOpenSearchVersions).describe('custom error responses', (engineVersion
         volumeSize: 100,
         volumeType: EbsDeviceVolumeType.GENERAL_PURPOSE_SSD,
       },
-    })).toThrow(/I3, R6GD, I4G, I4I, IM4GN and R7GD instance types do not support EBS storage volumes./);
+    })).toThrow(/I3, R6GD, I4G, I4I, I8G, IM4GN and R7GD instance types do not support EBS storage volumes./);
+  });
+
+  test.each([
+    'i3.2xlarge.search',
+    'r6gd.large.search',
+    'im4gn.2xlarge.search',
+    'i4g.large.search',
+    'i4i.xlarge.search',
+    'i8g.4xlarge.search',
+    'r7gd.xlarge.search',
+  ])('should not throw when %s instance type is specified without EBS enabled', (dataNodeInstanceType) => {
+    expect(() => new Domain(stack, 'Domain2', {
+      version: engineVersion,
+      capacity: {
+        dataNodeInstanceType,
+      },
+      ebs: { enabled: false },
+    })).not.toThrow();
   });
 
   test.each([
@@ -2058,7 +2077,7 @@ each(testedOpenSearchVersions).describe('custom error responses', (engineVersion
       capacity: {
         masterNodeInstanceType,
       },
-    })).toThrow(/EBS volumes are required when using instance types other than R3, I3, R6GD, I4G, I4I, IM4GN or R7GD./);
+    })).toThrow(/EBS volumes are required when using instance types other than R3, I3, R6GD, I4G, I4I, I8G, IM4GN or R7GD./);
   });
 
   test('can use compatible master instance types that does not have local storage when data node type is i3 or r6gd', () => {