Add push notifications for watched repos

It would be awesome to get push notifications for my watched repos. This is something that all other GitHub apps either don't have or are a paid feature.

I could definitely work on at least the iOS push notifications, though Android doesn't seem to be much different.

This might help: https://medium.com/differential/how-to-setup-push-notifications-in-react-native-ios-android-30ea0131355e

Start by reviewing the React Native push-notification setup described in the linked article and the existing watched-repository behavior in GitPoint. Define how watched-repository events should trigger notifications on both iOS and Android; done means users receive those notifications reliably on both platforms.

Rédigé par le modèle d'indexation à partir du texte de l'issue.