Fix the limited indexing setting name on the Elasticsearch page

What does this MR do?

An admin following the Elasticsearch page to turn on global search for limited indexing looks for a checkbox named Enable global search for limited indexing. The admin area has no option with that name. It labels the checkbox Use advanced search for global search when limited indexing is enabled, so this MR changes step 4 of the task to match. The checkbox was renamed in !188763 (merged), which updated doc/user/search/_index.md but not this page. The same edit adds the missing period to step 3, "Expand Advanced search".

The label comes from ee/app/views/admin/application_settings/_elasticsearch_form.html.haml:163, with its string at locale/gitlab.pot:91793, on master at 9d4cbde62f8. The old name survives only as the setting's description in the validator schema (ee/app/validators/json_schemas/application_setting_ee_search.json:49) and in the Korean translation (doc-locale/ko-kr/integration/advanced_search/elasticsearch.md:582), which this MR leaves alone.

Related issues

None.

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An AI coding assistant wrote this change. The assistant also checked the label against the files cited above and ran Vale, markdownlint-cli2 and the documentation link check on the changed page in a local checkout of master.