Add limit to Discover ES|QL queries to remove deprecation warnings (#202735)

## Summary

Resolves #196491.

Adds a `LIMIT` to our ES|QL Discover tests. Without the `LIMIT` we are
getting the following deprecation messages:

> Elasticsearch deprecation: 299
Elasticsearch-9.0.0-c74c06daee0583562c82597b19178268b9f415e5 "No limit
defined, adding default limit of [1000]"

### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

Author: lukasolson

test/functional/apps/discover/esql/_esql_columns.ts

@@ -181,14 +181,16 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
     });
 
     it('should reset columns if available fields or index pattern are different in transformational query', async () => {
-      await monacoEditor.setCodeEditorValue('from logstash-* | keep ip, @timestamp');
+      await monacoEditor.setCodeEditorValue('from logstash-* | keep ip, @timestamp | limit 500');
       await testSubjects.click('querySubmitButton');
       await header.waitUntilLoadingHasFinished();
       await discover.waitUntilSearchingHasFinished();
       expect(await dataGrid.getHeaderFields()).to.eql(['ip', '@timestamp']);
 
       // reset columns if available fields are different
-      await monacoEditor.setCodeEditorValue('from logstash-* | keep ip, @timestamp, bytes');
+      await monacoEditor.setCodeEditorValue(
+        'from logstash-* | keep ip, @timestamp, bytes | limit 500'
+      );
       await testSubjects.click('querySubmitButton');
       await header.waitUntilLoadingHasFinished();
       await discover.waitUntilSearchingHasFinished();