[8.14] [Playground] UI copy rework (#182659) (#183234)

# Backport

This will backport the following commits from `main` to `8.14`:
- [[Playground] UI copy rework
(#182659)](#182659)

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

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

<!--BACKPORT [{"author":{"name":"Liam
Thompson","email":"32779855+leemthompo@users.noreply.github.com"},"sourceCommit":{"committedDate":"2024-05-06T12:28:38Z","message":"[Playground]
UI copy rework
(#182659)","sha":"801c325b9538daf1255b70597ae6083417e56bdd","branchLabelMapping":{"^v8.15.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","Team:EnterpriseSearch","v8.14.0","v8.15.0"],"number":182659,"url":"#182659
UI copy rework
(#182659)","sha":"801c325b9538daf1255b70597ae6083417e56bdd"}},"sourceBranch":"main","suggestedTargetBranches":["8.14"],"targetPullRequestStates":[{"branch":"8.14","label":"v8.14.0","labelRegex":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"main","label":"v8.15.0","labelRegex":"^v8.15.0$","isSourceBranch":true,"state":"MERGED","url":"#182659
UI copy rework
(#182659)","sha":"801c325b9538daf1255b70597ae6083417e56bdd"}}]}]
BACKPORT-->

x-pack/plugins/search_playground/public/components/edit_context/edit_context_flyout.tsx

@@ -124,7 +124,7 @@ export const EditContextFlyout: React.FC<EditContextFlyoutProps> = ({ onClose })
                   label={i18n.translate(
                     'xpack.searchPlayground.editContext.flyout.docsRetrievedCount',
                     {
-                      defaultMessage: 'Number of documents to retrieve',
+                      defaultMessage: 'Number of documents sent to LLM',
                     }
                   )}
                 >