Prevent auto initialization

[msimkunas]

For privacy purposes there should be a way to leverage the opt-in functionality of FCM as described in the official Firebase docs (see section "Prevent auto initialization").

This would require adding a setAutoInitEnabled or some such method.

[chemerisuk]

@msimkunas it makes sense to add such feature. Let me know If you can help with the implementation or sponsor development.

[soerenBoisen]

Hello @chemerisuk ,
I'm looking into creating a pull request for this feature, since I also need it.

I assume that you will be against completely disabling auto initialization? In the brave new post GDPR and post CCPA world and "privacy by default", it would make a lot of sense to force manual initialization, but I understand the backwards compatibility concerns of such a change.