docs: rewrite old home, fix v0.1 infinite redirect (#21936)

docs/vercel.json

@@ -3,6 +3,10 @@
   "outputDirectory": "build",
   "trailingSlash": true,
   "rewrites": [
+    {
+      "source": "/v0.1",
+      "destination": "https://langchain-v01.vercel.app/v0.1"
+    },
     {
       "source": "/v0.1/:path(.*/?)*",
       "destination": "https://langchain-v01.vercel.app/v0.1/:path*"
@@ -25,6 +29,10 @@
       "source": "/docs(/?)",
       "destination": "/v0.2/docs/introduction/"
     },
+    {
+      "source": "/docs/get_started/introduction(/?)",
+      "destination": "/v0.2/docs/introduction/"
+    },
     {
       "source": "/docs/:path(.*/?)*",
       "destination": "/v0.1/docs/:path*"