docs: add firebase, elastic, and saas categories

website/i18n/en.json

@@ -32,6 +32,9 @@
       "nodes/azure": {
         "title": "Azure"
       },
+      "nodes/elastic": {
+        "title": "Elastic"
+      },
       "nodes/firebase": {
         "title": "Firebase"
       },

website/sidebars.json

@@ -18,7 +18,10 @@
       "nodes/k8s",
       "nodes/alibabacloud",
       "nodes/oci",
-      "nodes/programming"
+      "nodes/programming",
+      "nodes/firebase",
+      "nodes/saas",
+      "nodes/elastic"
     ]
   }
 }