[FR] Add option not Adding Crashlytics Run Script to the Xcode project's Build Phases

### Feature proposal

I am using the Unity project as a library that is part of my app which has imported the `FirebaseCrashlytics` and added the crashlytics run script. Therefore, I would like to get rid of the related run script generated from Unity build. Although I can remove if manually in XCode, I still would like to know if we can have an option to determine adding the Crashlytics Run Script or not?