Move Flipper integration to a separate Gradle module inside `ReactAndroid` (#37688)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/37688

This moves the `ReactNativeFlipper` classes used to configure Flipper on Android from the template to
a separate Gradle artifact that will be published under the coordinates:
```
com.facebook.react:flipper-integration:0.73.x
```

This reduces the footprint of Flipper on the app template and makes easier for user on 0.73 to migrate
to Kotlin (as they will now have to migrate only 2 files rather than 4).

Changelog:
[Android] [Changed] - Move Flipper integration to a separate Gradle module inside `ReactAndroid`

Reviewed By: huntie

Differential Revision: D46441588

fbshipit-source-id: e197f29b7386b52091b8d38ed09bbd8f74a997df