[DOCS] Document `doc_as_upsert` does not support ingest pipelines (#57649) (#57782)

Co-authored-by: James Rodewig <james.rodewig@elastic.co>

Co-authored-by: Asfaloth <asfalots@users.noreply.github.com>

docs/reference/docs/update.asciidoc

@@ -332,3 +332,7 @@ POST test/_update/1
 }
 --------------------------------------------------
 // TEST[continued]
+[NOTE]
+====
+Using <<ingest,ingest pipelines>> with `doc_as_upsert` is not supported.
+====