download hermes-engine when the configuration change (#37850)

Summary:
Currently, we ask users to reinstall the pods using the `PRODUCTION` flag when they want to either profile their app or prepare a release.

This way of working with the Release mode is not standard. One of the reason why we introduced it was to provide a different binary for Hermes and reinstalling the pods was the quickest way.

With this change, we are deferring the decision on when Hermes should be installed for apps to the moment where the app is actually build by the system.

These changes are not applied to Nightlies, when a specific tarball is passed to the cocoapods using the `HERMES_ENGINE_TARBALL_PATH` env var, and when hermes is built from source as in these scenarios we are usually not interested in building for Release.

The system is also smart enough not to redownload the tarball if the configuration does not change. It assumes that the default configuration when the pods are installed for the first time is Debug.

## Changelog:

[IOS] [CHANGED] - Download the right `hermes-engine` configuration at build time.

Pull Request resolved: https://github.com/facebook/react-native/pull/37850

Test Plan:
- CircleCI green for the Release template jobs
- Tested locally modifying the `hermes-utils` to force specific versions.
- Tested locally with RNTestProject

Reviewed By: dmytrorykun

Differential Revision: D46687390

Pulled By: cipolleschi

fbshipit-source-id: 375406e0ab351a5d1f5d5146e724f5ed0cd77949