fix the 404 link for the original conversation variable content (#590)

Co-authored-by: Riskey <riskey47@dify.ai>

Author: RiskeyL

docs.json

@@ -4142,6 +4142,18 @@
     ]
   },
   "redirects": [
+    {
+      "source": "/en/guides/workflow/variables#conversation-variables",
+      "destination": "/en/use-dify/getting-started/key-concepts#variables"
+    },
+    {
+      "source": "/zh-hans/guides/workflow/variables#会话变量",
+      "destination": "/zh/use-dify/getting-started/key-concepts#变量"
+    },
+    {
+      "source": "/ja-jp/guides/workflow/variables#会話変数",
+      "destination": "/ja/use-dify/getting-started/key-concepts#変数"
+    },
     {
       "source": "/en/guides/workflow/node/start",
       "destination": "/en/use-dify/getting-started/key-concepts#workflow"