Enable metro hmr server in local-cli (#20605)

Summary:
The `hmrEnabled` flag was not passed to the metro runServer config which caused HMR to be broken.
Pull Request resolved: https://github.com/facebook/react-native/pull/20605

Differential Revision: D9272070

Pulled By: hramos

fbshipit-source-id: 3765031d9e7806be11781fba92663ce7c4ff2ffb

local-cli/server/runServer.js

@@ -65,6 +65,7 @@ async function runServer(args: Args, config: ConfigT) {
     secure: args.https,
     secureCert: args.cert,
     secureKey: args.key,
+    hmrEnabled: true,
   });
 
   const wsProxy = webSocketProxy.attachToServer(