Improve metro waiting times in E2E (#48281)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/48281

While working on Maestro E2E I realized that we were waiting for Metro to start even when metro was not running.

This moves the waiting only when metro is actually started.

I also added another waiting point as it takes several seconds for the app to load the bundle from metro the first time. Subsequent attempts are faster as the metro cache is warm.

## Changelog:
[Internal] - Improve metro waiting times in E2E

Reviewed By: fabriziocucci

Differential Revision: D67273648

fbshipit-source-id: 912be4d14869c8ce87d7c4e4f7ee37b643f5845c