Summary:
As described in DevSettingsActivity, it should be added to the apps
debug/ instead of main/ manifest.
## Changelog
Android Changed - Move DevSettingsActivity from `main` to `debug` manifest
Pull Request resolved: https://github.com/facebook/react-native/pull/28770
Test Plan: Tested locally by building example app
Differential Revision: D21281922
Pulled By: shergin
fbshipit-source-id: ec4dc7c0ac54367aa38cca5b4146ef71cf18b73b
