[Security Solution][Exceptions] - Updates exception item find sort field (#76685)

## Summary

This is a bug that was introduced by moi in 76537. This previous PR added a sort_field and sort_order to the call for fetching exception lists' items so that the exception item order in the viewer wouldn't jump around any time there was an update. I noticed however that when a rule had both endpoint and detection lists associated with it, when trying to fetch items from both types of lists, the following error shows:

```
"Unable to sort multiple types by field created_at, not a root property"
```

Author: yctercero

x-pack/plugins/lists/public/exceptions/api.test.ts

@@ -375,7 +375,7 @@ describe('Exceptions Lists API', () => {
           namespace_type: 'single,single',
           page: '1',
           per_page: '20',
-          sort_field: 'created_at',
+          sort_field: 'exception-list.created_at',
           sort_order: 'desc',
         },
         signal: abortCtrl.signal,
@@ -408,7 +408,7 @@ describe('Exceptions Lists API', () => {
           namespace_type: 'single',
           page: '1',
           per_page: '20',
-          sort_field: 'created_at',
+          sort_field: 'exception-list.created_at',
           sort_order: 'desc',
         },
         signal: abortCtrl.signal,
@@ -441,7 +441,7 @@ describe('Exceptions Lists API', () => {
           namespace_type: 'agnostic',
           page: '1',
           per_page: '20',
-          sort_field: 'created_at',
+          sort_field: 'exception-list.created_at',
           sort_order: 'desc',
         },
         signal: abortCtrl.signal,
@@ -474,7 +474,7 @@ describe('Exceptions Lists API', () => {
           namespace_type: 'agnostic',
           page: '1',
           per_page: '20',
-          sort_field: 'created_at',
+          sort_field: 'exception-list.created_at',
           sort_order: 'desc',
         },
         signal: abortCtrl.signal,
@@ -508,7 +508,7 @@ describe('Exceptions Lists API', () => {
           namespace_type: 'agnostic',
           page: '1',
           per_page: '20',
-          sort_field: 'created_at',
+          sort_field: 'exception-list.created_at',
           sort_order: 'desc',
         },
         signal: abortCtrl.signal,

x-pack/plugins/lists/public/exceptions/api.ts

@@ -288,7 +288,7 @@ export const fetchExceptionListsItemsByListIds = async ({
     namespace_type: namespaceTypes.join(','),
     page: pagination.page ? `${pagination.page}` : '1',
     per_page: pagination.perPage ? `${pagination.perPage}` : '20',
-    sort_field: 'created_at',
+    sort_field: 'exception-list.created_at',
     sort_order: 'desc',
     ...(filters.trim() !== '' ? { filter: filters } : {}),
   };