[ios] App extensions support

[vomchik]

I've split a module for two interfaces that allowed to use config service without the react dependency.
That will helps to use a module in an ios app extensions.

[height]

Link Height tasks by mentioning a task ID in the pull request title or description, commit messages, or comments.

You can also use "Close T-X" to automatically close a task when the pull request is merged.

[luancurti]

Thanks!

[Taylor123]

@vomchik is there any other configuration for the Podfile aside from

pod 'react-native-config', :path => '../node_modules/react-native-config'

I continue to run into build issues for an extension since RNConfig relies on React as a cocoapod dependency, which then attempts to build RCTLinking that has source code not suitable for an extension