[8.10] [Discover] Fix ESQL flaky test (#166249) (#166586)

# Backport

This will backport the following commits from `main` to `8.10`:
- [[Discover] Fix ESQL flaky test
(#166249)](#166249)

<!--- Backport version: 8.9.8 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Julia
Rechkunova","email":"julia.rechkunova@elastic.co"},"sourceCommit":{"committedDate":"2023-09-18T07:35:12Z","message":"[Discover]
Fix ESQL flaky test (#166249)\n\n- Closes
#165860
Fix ESQL flaky test (#166249)\n\n- Closes
#165860
Fix ESQL flaky test (#166249)\n\n- Closes
#165860"}}]}]
BACKPORT-->

test/functional/apps/discover/group2/_sql_view.ts

@@ -94,6 +94,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
         await monacoEditor.setCodeEditorValue(testQuery);
         await testSubjects.click('querySubmitButton');
         await PageObjects.header.waitUntilLoadingHasFinished();
+        await PageObjects.discover.waitUntilSearchingHasFinished();
         // here Lens suggests a heatmap so it is rendered
         expect(await testSubjects.exists('unifiedHistogramChart')).to.be(true);
         expect(await testSubjects.exists('heatmapChart')).to.be(true);
@@ -110,16 +111,19 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
         await monacoEditor.setCodeEditorValue(testQuery);
         await testSubjects.click('querySubmitButton');
         await PageObjects.header.waitUntilLoadingHasFinished();
+        await PageObjects.discover.waitUntilSearchingHasFinished();
         let cell = await dataGrid.getCellElement(0, 4);
         expect(await cell.getVisibleText()).to.be('2269');
         await PageObjects.timePicker.setAbsoluteRange(
           'Sep 19, 2015 @ 06:31:44.000',
           'Sep 19, 2015 @ 06:31:44.000'
         );
         await PageObjects.header.waitUntilLoadingHasFinished();
+        await PageObjects.discover.waitUntilSearchingHasFinished();
         expect(await testSubjects.exists('discoverNoResults')).to.be(true);
         await PageObjects.timePicker.setDefaultAbsoluteRange();
         await PageObjects.header.waitUntilLoadingHasFinished();
+        await PageObjects.discover.waitUntilSearchingHasFinished();
         cell = await dataGrid.getCellElement(0, 4);
         expect(await cell.getVisibleText()).to.be('2269');
       });