docs(firebase_remote_config): add documentation what is returned when the key does not exist for getBool, getInt, getDouble and getString

[nilsreichardt]

Description

You might expect that the methods are returning null or throwing an exception. But Firebase returns default values. Therefore, I added the values which are returned when the key for the methods does not exist.

Got the values from here:https://firebase.google.com/docs/reference/android/com/google/firebase/remoteconfig/FirebaseRemoteConfig

Zapp Online Demo for default values: https://zapp.run/edit/firebaseremoteconfig-3014-zd6206xrd630?entry=lib/main.dart&file=lib/main.dart

Related Issues

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[russellwheatley]

I wonder if we could add e2e tests to show this is cross platform 🤔

[nilsreichardt]

I wonder if we could add e2e tests to show this is cross platform 🤔

@russellwheatley #10723 adds tests for this :)