ui-next: add sample plugin

packages/ui-next-plugin-sample/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "@hydrooj/ui-next-plugin-sample",
+  "dependencies": {
+    "@hydrooj/ui-next": "workspace:*"
+  }
+}

packages/ui-next-plugin-sample/ui/before.tsx

@@ -0,0 +1,4 @@
+export default function BeforeComponent() {
+    console.log('before app');
+    return <div>before app via @hydrooj/ui-next-plugin-sample</div>;
+}

packages/ui-next-plugin-sample/ui/index.ts

@@ -0,0 +1,6 @@
+import type { PluginAPI } from '@hydrooj/ui-next';
+import BeforeComponent from './before';
+
+export function setup(api: PluginAPI) {
+    api.before('page:app', BeforeComponent);
+}