[DOCS] Build Elasticsearch Reference from elasticsearch repo (#28469)

docs/reference/index.x.asciidoc

@@ -0,0 +1,12 @@
+[[elasticsearch-reference]]
+= Elasticsearch Reference
+
+:include-xpack:         true
+:es-test-dir:           {docdir}/../src/test
+:plugins-examples-dir:  {docdir}/../../plugins/examples
+:xes-repo-dir:          {docdir}/../../../elasticsearch-extra/x-pack-elasticsearch/docs/{lang}
+:es-repo-dir:           {docdir}
+
+
+include::../Versions.asciidoc[]
+include::{xes-repo-dir}/index.asciidoc[]