[ML] Fix page header right side items flex responsiveness (#198625)

## Summary

Partially addresses https://github.com/elastic/kibana/issues/197892, but
not fully - https://github.com/elastic/eui/pull/8109 and
https://github.com/elastic/eui/pull/8110 will need to be merged in first
and in Kibana main as well. We can hold this PR until then if desired to
confirm that the final UI/responsive UX works as expected.

| Before | After |
|--------|--------|
| <img width="974" alt=""
src="https://github.com/user-attachments/assets/c081fbfe-d2ec-4797-addb-3c9ecbc3085d">
| <img width="983" alt=""
src="https://github.com/user-attachments/assets/6152be23-f2b7-4712-8e53-e368db606418">
|

### Checklist

- [x] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [x] Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))
- [x] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [x] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)

x-pack/plugins/aiops/public/components/page_header/page_header.tsx

@@ -9,7 +9,7 @@ import { css } from '@emotion/react';
 import type { FC } from 'react';
 import React, { useCallback, useMemo } from 'react';
 
-import { EuiFlexGroup, EuiFlexItem, EuiPageHeader } from '@elastic/eui';
+import { EuiPageHeader } from '@elastic/eui';
 
 import { useUrlState } from '@kbn/ml-url-state';
 import { useStorage } from '@kbn/ml-local-storage';
@@ -71,29 +71,29 @@ export const PageHeader: FC = () => {
   return (
     <EuiPageHeader
       pageTitle={<div css={dataViewTitleHeader}>{dataView.getName()}</div>}
+      rightSideGroupProps={{
+        gutterSize: 's',
+        'data-test-subj': 'aiopsTimeRangeSelectorSection',
+      }}
       rightSideItems={[
-        <EuiFlexGroup gutterSize="s" data-test-subj="aiopsTimeRangeSelectorSection">
-          {hasValidTimeField ? (
-            <EuiFlexItem grow={false}>
-              <FullTimeRangeSelector
-                frozenDataPreference={frozenDataPreference}
-                setFrozenDataPreference={setFrozenDataPreference}
-                dataView={dataView}
-                query={undefined}
-                disabled={false}
-                timefilter={timefilter}
-                callback={updateTimeState}
-              />
-            </EuiFlexItem>
-          ) : null}
-          <DatePickerWrapper
-            isAutoRefreshOnly={!hasValidTimeField}
-            showRefresh={!hasValidTimeField}
-            width="full"
-            flexGroup={false}
+        <DatePickerWrapper
+          isAutoRefreshOnly={!hasValidTimeField}
+          showRefresh={!hasValidTimeField}
+          width="full"
+          flexGroup={!hasValidTimeField}
+        />,
+        hasValidTimeField && (
+          <FullTimeRangeSelector
+            frozenDataPreference={frozenDataPreference}
+            setFrozenDataPreference={setFrozenDataPreference}
+            dataView={dataView}
+            query={undefined}
+            disabled={false}
+            timefilter={timefilter}
+            callback={updateTimeState}
           />
-        </EuiFlexGroup>,
-      ]}
+        ),
+      ].filter(Boolean)}
     />
   );
 };

x-pack/plugins/data_visualizer/public/application/data_drift/data_drift_page.tsx

@@ -106,31 +106,31 @@ export const PageHeader: FC<PageHeaderProps> = ({ onRefresh, needsUpdate }) => {
           {dataView.getName()}
         </div>
       }
+      rightSideGroupProps={{
+        gutterSize: 's',
+        'data-test-subj': 'dataComparisonTimeRangeSelectorSection',
+      }}
       rightSideItems={[
-        <EuiFlexGroup gutterSize="s" data-test-subj="dataComparisonTimeRangeSelectorSection">
-          {hasValidTimeField ? (
-            <EuiFlexItem grow={false}>
-              <FullTimeRangeSelector
-                frozenDataPreference={frozenDataPreference}
-                setFrozenDataPreference={setFrozenDataPreference}
-                dataView={dataView}
-                query={undefined}
-                disabled={false}
-                timefilter={timefilter}
-                callback={updateTimeState}
-              />
-            </EuiFlexItem>
-          ) : null}
-          <DatePickerWrapper
-            isAutoRefreshOnly={!hasValidTimeField}
-            showRefresh={!hasValidTimeField}
-            width="full"
-            flexGroup={false}
-            onRefresh={onRefresh}
-            needsUpdate={needsUpdate}
+        <DatePickerWrapper
+          isAutoRefreshOnly={!hasValidTimeField}
+          showRefresh={!hasValidTimeField}
+          width="full"
+          flexGroup={!hasValidTimeField}
+          onRefresh={onRefresh}
+          needsUpdate={needsUpdate}
+        />,
+        hasValidTimeField && (
+          <FullTimeRangeSelector
+            frozenDataPreference={frozenDataPreference}
+            setFrozenDataPreference={setFrozenDataPreference}
+            dataView={dataView}
+            query={undefined}
+            disabled={false}
+            timefilter={timefilter}
+            callback={updateTimeState}
           />
-        </EuiFlexGroup>,
-      ]}
+        ),
+      ].filter(Boolean)}
     />
   );
 };