[WEB-1657] dev: admin application code structuring. (#4867)

* [WEB-1657] dev: admin application code structuring.

* chore: update mobx-react-lite import to mobx-react.

admin/core/components/instance/instance-not-ready.tsx

@@ -0,0 +1,30 @@
+"use client";
+
+import { FC } from "react";
+import Image from "next/image";
+import Link from "next/link";
+import { Button } from "@plane/ui";
+// assets
+import PlaneTakeOffImage from "@/public/images/plane-takeoff.png";
+
+export const InstanceNotReady: FC = () => (
+  <div className="h-full w-full relative container px-5 mx-auto flex justify-center items-center">
+    <div className="w-auto max-w-2xl relative space-y-8 py-10">
+      <div className="relative flex flex-col justify-center items-center space-y-4">
+        <h1 className="text-3xl font-bold pb-3">Welcome aboard Plane!</h1>
+        <Image src={PlaneTakeOffImage} alt="Plane Logo" />
+        <p className="font-medium text-base text-onboarding-text-400">
+          Get started by setting up your instance and workspace
+        </p>
+      </div>
+
+      <div>
+        <Link href={"/setup/?auth_enabled=0"}>
+          <Button size="lg" className="w-full">
+            Get started
+          </Button>
+        </Link>
+      </div>
+    </div>
+  </div>
+);