Build Release version for RNTester to speed-up E2E (#48443)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/48443

This change makes sure we build the Release variant of RNTester so we can store the generated app as an artifact and forward it to the E2E tests.

## Context

While looking at the recent failures of the E2E tests, I realized that the Hermes, NewArch, Debug variant often fails to build, not to test, for some misconfiguration.

I also realized that we are already building that varaint successfully once, so why not reuse it? To reuse prebuilds, we need a few steps:

1. make sure we build all the variants we need
2. store the .app file as an artifact
3. download the artifact and use it in the E2E tests

## Changelog:
[Internal] - Build release variant for RNTester

Reviewed By: cortinico

Differential Revision: D67760372

fbshipit-source-id: 02cc9ec64d5a7b4fa2ad05bca6aa91a69b2b5907