[Security Solution][Detection Engine] fixes empty item_id in exceptio…

…n item update request (#194172)

## Summary

 - fixes #191315 in 8.15

When trying to update exception item with empty item_id, it will return
error


```JSON
{
  "statusCode": 400,
  "error": "Bad Request",
  "message": "[request body]: Invalid value \"\" supplied to \"item_id\""
}
```

<img width="2493" alt="Screenshot 2024-09-26 at 16 05 51"
src="https://github.com/user-attachments/assets/f68bfe94-4a4f-4d44-8255-7ae7fda8563e">


8.16(main) was fixed earlier:
#191315 (comment)

packages/kbn-securitysolution-io-ts-list-types/src/request/update_exception_list_item_schema/index.ts

@@ -20,6 +20,7 @@ import { description } from '../../common/description';
 import { name } from '../../common/name';
 import { _version } from '../../common/underscore_version';
 import { id } from '../../common/id';
+import { item_id } from '../../common/item_id';
 import { meta } from '../../common/meta';
 import { namespace_type } from '../../common/namespace_type';
 import { ExpireTimeOrUndefined, expireTimeOrUndefined } from '../../common';
@@ -39,7 +40,7 @@ export const updateExceptionListItemSchema = t.intersection([
       comments: DefaultUpdateCommentsArray, // defaults to empty array if not set during decode
       expire_time: expireTimeOrUndefined,
       id, // defaults to undefined if not set during decode
-      item_id: t.union([t.string, t.undefined]),
+      item_id,
       meta, // defaults to undefined if not set during decode
       namespace_type, // defaults to 'single' if not set during decode
       os_types: osTypeArrayOrUndefined, // defaults to empty array if not set during decode