docs: Add policy engine documentation and update sidebar (#12240)

docs/sidebar.json

@@ -116,6 +116,10 @@
       {
         "label": "Memory Import Processor",
         "slug": "docs/core/memport"
+      },
+      {
+        "label": "Policy Engine",
+        "slug": "docs/core/policy-engine"
       }
     ]
   },