Migrate helloworld to use `{usesCleartextTraffic}` manifest placeholder (#52647)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52647

This removes the need to specify 2 Manifests for apps and we can just use the `main` manifes to toggle if `usesCleartextTraffic` should be enabled or not.

This will have to be replicated in the template repository.

Changelog:
[Android] [Added] - Add support to specify a single Manifest rather than 2 (main/debug) by using the `usesCleartextTraffic` manifest placeholder which is autoconfigured by RNGP.

Reviewed By: cipolleschi

Differential Revision: D78425139

fbshipit-source-id: 9173a014b387d5aed5f7087fa69b7bd49c220f2c