Use RNTester App downloaded from CI instead of building (#48637)

Summary:
This change improves the E2E testing by downloading the iOS RNTesterApp that is built in CI instead of building it locally. This should let us save 10 to 20 minutes when we test a new release.

## Changelog:
[Internal] - Use the RNTester app built in CI for release testing on iOS

Pull Request resolved: https://github.com/facebook/react-native/pull/48637

Test Plan:
- build the app in ci
- run `yarn test-e2e-local -c <my-token>` and `yarn test-e2e-local -h false -c <my-token>` and verify that the iOS app is not built, but run in the simulator

Reviewed By: cortinico

Differential Revision: D68161477

Pulled By: cipolleschi

fbshipit-source-id: 577d110f9ff0197a2d3348a08a60e60a4d0a752b