feat: add Passenger-compatible server.js startup file for o2switch

Passenger runs a literal JS entry file, not the next start CLI or an
npm script, so a custom server was needed for cPanel's Node.js App
startup file field.

server.js

@@ -0,0 +1,14 @@
+const { createServer } = require('http')
+const next = require('next')
+
+const port = parseInt(process.env.PORT || '3000', 10)
+const app = next({ dev: false })
+const handle = app.getRequestHandler()
+
+app.prepare().then(() => {
+  createServer((req, res) => {
+    handle(req, res)
+  }).listen(port, () => {
+    console.log(`> Ready on port ${port}`)
+  })
+})