[Platform:StackManagement:Data Set Quality page] Enhance accessibility of filter bar (#241012)

Closes #219218 

## Summary

Improves accessibility of the Dataset Quality filter bar by introducing
a more specific aria-label for screen readers.

## Changes
- Add a separate ariaLabel i18n key
- Update aria-label prop on EuiFieldSearch using this label

## Steps to reproduce
- Open NVDA Speech Viewer
- Navigate to the Data Set Quality (Go to the Discover tab on the
left-side navigation -> Press "Data sets" on the top right)
- Focus on the filter bar, preferably with keyboard controls

## Expected Result 

<img width="689" height="449" alt="Screenshot 2025-10-29 110341"
src="https://github.com/user-attachments/assets/a530ef6c-198f-45ec-a789-8fb4698664a6"
/>

Author: jorgeoliveira117

x-pack/platform/plugins/shared/dataset_quality/public/components/dataset_quality/filters/filter_bar.tsx

@@ -14,6 +14,10 @@ const placeholder = i18n.translate('xpack.datasetQuality.filterBar.placeholder',
   defaultMessage: 'Filter data sets',
 });
 
+const ariaLabel = i18n.translate('xpack.datasetQuality.filterBar.ariaLabel', {
+  defaultMessage: 'Type a data set name',
+});
+
 export interface FilterBarComponentProps {
   query?: string;
   onQueryChange: (query: string) => void;
@@ -35,7 +39,7 @@ export const FilterBar = ({ query, onQueryChange }: FilterBarComponentProps) =>
       value={query ?? ''}
       onChange={onChange}
       isClearable={true}
-      aria-label={placeholder}
+      aria-label={ariaLabel}
     />
   );
 };