[DOCS] Link to preview data frame analytics API (#1590) (#1595)

Author: lcawl

docs/en/stack/ml/df-analytics/ml-dfanalytics-apis.asciidoc

@@ -27,6 +27,7 @@ All the trained models endpoints have the following base:
 // NOTCONSOLE
 
 
+* {ref}/preview-dfanalytics.html[Preview {dfanalytics}]
 * {ref}/put-dfanalytics.html[Create {dfanalytics-jobs}]
 * {ref}/update-dfanalytics.html[Update {dfanalytics-jobs}]
 * {ref}/delete-dfanalytics.html[Delete {dfanalytics-jobs}]