[9.0] [a11y][ml] Add visually hidden label for screenreader for open documentation button (#224047) (#224240)

# Backport

This will backport the following commits from `main` to `9.0`:
- [[a11y][ml] Add visually hidden label for screenreader for open
documentation button
(#224047)](https://github.com/elastic/kibana/pull/224047)

<!--- Backport version: 9.6.6 -->

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

<!--BACKPORT [{"author":{"name":"Paulina
Shakirova","email":"paulina.shakirova@elastic.co"},"sourceCommit":{"committedDate":"2025-06-17T11:52:24Z","message":"[a11y][ml]
Add visually hidden label for screenreader for open documentation button
(#224047)\n\nThis PR resolves [[ML] ES|QL Data Visualizer: The button to
access es|ql\nquick reference is missing
discernible\ntext](https://github.com/elastic/kibana/issues/217094)
issue.\n\n\nhttps://github.com/user-attachments/assets/09e18f9f-eb06-4468-bc72-c0c4e46a642e","sha":"f03c565daf7796fc79b70fc9f540f86d44d224f2","branchLabelMapping":{"^v9.1.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","backport:all-open","a11y","v9.1.0"],"title":"[a11y][ml]
Add visually hidden label for screenreader for open documentation
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Add visually hidden label for screenreader for open documentation button
(#224047)\n\nThis PR resolves [[ML] ES|QL Data Visualizer: The button to
access es|ql\nquick reference is missing
discernible\ntext](https://github.com/elastic/kibana/issues/217094)
issue.\n\n\nhttps://github.com/user-attachments/assets/09e18f9f-eb06-4468-bc72-c0c4e46a642e","sha":"f03c565daf7796fc79b70fc9f540f86d44d224f2"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/224047","number":224047,"mergeCommit":{"message":"[a11y][ml]
Add visually hidden label for screenreader for open documentation button
(#224047)\n\nThis PR resolves [[ML] ES|QL Data Visualizer: The button to
access es|ql\nquick reference is missing
discernible\ntext](https://github.com/elastic/kibana/issues/217094)
issue.\n\n\nhttps://github.com/user-attachments/assets/09e18f9f-eb06-4468-bc72-c0c4e46a642e","sha":"f03c565daf7796fc79b70fc9f540f86d44d224f2"}}]}]
BACKPORT-->

Co-authored-by: Paulina Shakirova <paulina.shakirova@elastic.co>

src/platform/packages/private/kbn-esql-editor/src/editor_footer/index.tsx

@@ -270,6 +270,9 @@ export const EditorFooter = memo(function EditorFooter({
                     data-test-subj="ESQLEditor-documentation"
                     size="m"
                     onClick={() => toggleLanguageComponent()}
+                    aria-label={i18n.translate('esqlEditor.query.documentationAriaLabel', {
+                      defaultMessage: 'Open documentation',
+                    })}
                     css={css`
                       cursor: pointer;
                     `}