Include a link to downsampling a TSDS using DSL document (#117510) (#117580)

docs/reference/data-streams/tsds.asciidoc

@@ -339,4 +339,5 @@ include::tsds-index-settings.asciidoc[]
 include::downsampling.asciidoc[]
 include::downsampling-ilm.asciidoc[]
 include::downsampling-manual.asciidoc[]
+include::downsampling-dsl.asciidoc[]
 include::tsds-reindex.asciidoc[]