engine: add target qualifier for engine api layout cascade

Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>

content/reference/api/engine/version/_index.md

@@ -5,6 +5,8 @@ build:
 sidebar:
   reverse: true
 cascade:
+  _target:
+    path: /reference/api/engine/version/**
   description: Reference documentation and Swagger (OpenAPI) specification for the Docker Engine API.
   layout: api
 ---