[ObsUX][A11y] Add area label to comparison drop down (#215664)

Closes #210254

Before

<img width="1494" alt="Screenshot 2025-03-24 at 10 51 01"
src="https://github.com/user-attachments/assets/872ca24d-8087-4261-bdf0-19107b13d01a"
/>

After

<img width="1494" alt="Screenshot 2025-03-24 at 10 49 51"
src="https://github.com/user-attachments/assets/6d840f70-41b3-4891-ab91-cf99f3c6a93e"
/>

Author: MiriamAparicio

x-pack/solutions/observability/plugins/apm/public/components/shared/time_comparison/index.tsx

@@ -99,6 +99,9 @@ export function TimeComparison() {
 
   return (
     <EuiSelect
+      aria-label={i18n.translate('xpack.apm.timeComparison.euiSelect.seletTimeComparisonLabel', {
+        defaultMessage: 'Select time comparison options',
+      })}
       fullWidth={isSmall || isMedium}
       data-test-subj="comparisonSelect"
       disabled={comparisonEnabled === false}