[cloud_functions]Add region support for cloud functions

[Knupper]

Hey,

here my implementation to add region support for cloud_functions (see #24333).

King regards

Max

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[Knupper]

I signed it!

[googlebot]

CLAs look good, thanks!

[Knupper]

Any updates or feedback is appreciated.

[slightfoot]

@Knupper I checked FirebaseApp hoping we got a default region for the project through in google-services.json but we don't. With Firestore now going multi-region it might be worth combining efforts here if there is a more direct route.

Other change that might be worth making is that FirebaseApp should be able to be passed in. This might already be in another PR. Might be worth making another PR for that however.

References to how Firestore plugin does it.
https://github.com/flutter/plugins/blob/master/packages/cloud_firestore/lib/src/firestore.dart#L132
https://github.com/flutter/plugins/blob/master/packages/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/cloudfirestore/CloudFirestorePlugin.java#L80
https://firebase.google.com/docs/reference/android/com/google/firebase/functions/FirebaseFunctions.html#getInstance%28com.google.firebase.FirebaseApp%2C+java.lang.String%29

[slightfoot]

@kroikie hey Arthur, Needs a second review and I nominate you 😁 If your happy with it, then I leave it for you to merge and release 👍

[Knupper]

@slightfoot can be closed, we have region support now :)

[slightfoot]

Looks like PR #1210 has superseded this one with support for multiple Apps and Regions. Closing.

[dshukertjr]

Wait, so do we have region support for cloud functions plug in now? If it is, it is super unclear as to how to call functions in different regions.