docs: Mark ES|QL views note as available in serverless (#7437)

ES|QL views are now available in serverless as a preview feature
(Elasticsearch exposes the views API with @ServerlessScope(Scope.PUBLIC)
and stability: experimental; Kibana enabled views in serverless via
elastic/kibana#274819). Update the Discover editor note that describes
how views appear in the data source browser and autocomplete from
serverless: unavailable to serverless: preview. The behavior is
unchanged: views are surfaced through autocomplete but not the data
source browser.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: florent-leborgne

explore-analyze/discover/try-esql.md

@@ -106,7 +106,7 @@ When you write a query, the {{esql}} editor includes two interactive browsers th
 - **Fields browser**: lists fields for the data sources currently in your query and lets you insert one field at a time at the cursor position.
 
 :::{note}
-:applies_to: {stack: preview 9.4.0, serverless: unavailable}
+:applies_to: {stack: preview 9.4.0, serverless: preview}
 [{{esql}} views](elasticsearch://reference/query-languages/esql/esql-views.md) aren't shown in the data source browser but they're visible through the autocomplete menu suggestions.
 :::