Set standalone server default hostname to 0.0.0.0 (vercel#54445)

By default Next.js listens on localhost, platforms like Google Cloud Run and fly.io will fail to deploy apps that listen on `localhost`, Next.js should bind to `0.0.0.0` instead

Related to vercel#54342
Fixes vercel#49777
Fixes vercel#54133

packages/next/src/build/utils.ts

@@ -1984,7 +1984,7 @@ if (!process.env.NEXT_MANUAL_SIG_HANDLE) {
 }
 
 const currentPort = parseInt(process.env.PORT, 10) || 3000
-const hostname = process.env.HOSTNAME || 'localhost'
+const hostname = process.env.HOSTNAME || '0.0.0.0'
 
 let keepAliveTimeout = parseInt(process.env.KEEP_ALIVE_TIMEOUT, 10)
 const nextConfig = ${JSON.stringify({