Don't flash the performance monitor there's no metro connection (#54019)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/54019

Currently the performance monitor flickers on boot if there's no metro connection. This change checks first if we have a packager before enabling the monitor.

No metro connection:
{F1982423105}

Metro connection:
{F1982423112}

Changelog: [Internal]

Reviewed By: shwanton

Differential Revision: D83701372

fbshipit-source-id: d099880d3ab509942a937a6bde11ebdde13450cd