Update Gemini dev server and serve 4.17 (#5199)

* Update dev server and use 4.17

* Add Node.js 16 requirements

packages/embed/hostDevServer.mjs

@@ -0,0 +1,37 @@
+import express from 'express';
+import { createProxyMiddleware } from 'http-proxy-middleware';
+import { join } from 'path';
+import { fileURLToPath } from 'url';
+
+const { PORT = 5002 } = process.env;
+const DEFAULT_BOT_ID = 'webchat-mockbot';
+
+const app = express();
+
+app.get('/', async (_, res) => {
+  const tokenRes = await fetch('https://webchat-mockbot.azurewebsites.net/directline/token', { method: 'POST' });
+
+  if (!tokenRes.ok) {
+    return res.send(500);
+  }
+
+  const { token } = await tokenRes.json();
+
+  const redirectURL = new URL(DEFAULT_BOT_ID, 'http://localhost/embed/');
+
+  redirectURL.searchParams.set('b', DEFAULT_BOT_ID);
+  redirectURL.searchParams.set('t', token);
+
+  res.status(302);
+  res.header('location', redirectURL.pathname + redirectURL.search);
+
+  return res.end();
+});
+
+app.get('/embed/:bot', async (_, res) =>
+  res.setHeader('content-type', 'text/html').sendFile(join(fileURLToPath(import.meta.url), '../dist/gemini.html'))
+);
+
+app.get('/embed/:bot/config', createProxyMiddleware({ changeOrigin: true, target: 'https://webchat.botframework.com/' }));
+
+app.listen(PORT, () => console.log(`Embed dev server is listening to port ${PORT}`));