[FR] UI for disable/enable auto init in unity editor

* Firebase Component: Core

There is a setting that allow us to [Prevent auto initialization](https://firebase.google.com/docs/cloud-messaging/unity/client#prevent_auto_initialization). But I think firebase sdk can write/rewrite both xml and plist internally, isn't it?

So I wish that there would be a setting, just a toggle for enable/disable auto initialization somewhere, to insert this config into build process by firebase

Is it possible?