Add support for Firestore bundles

[aaronSig]

Cloud Firestore now supports generating document bundles that can be loaded into the clients.

Details here:
https://firebase.google.com/docs/firestore/bundles

Is there any work currently underway to implement this in RNFirebase?

If not I'm happy to help and submit a PR for this.

[mikehardy]

It's a feature we'd love to have but there is no progress yet. Do you have any time to work up a PR for it? I could collaborate with you to get it merged, and there is some existing work to base the feature on from the partner project FlutterFire - firebase/flutterfire#6037

If not, it may be some time but it will happen, it's an important feature yes

[kmsbernard]

If there is no work in progress yet, I'd like to implement the bundle API and make a PR for it. The work in FlutterFire seems very helpful for this.

[kmsbernard]

I've opened a draft PR: #6199

[mikehardy]

Ooooo - that's fantastic. This has been nagging at me - that we did not have it yet, it's a great cost optimization. Thanks for posting a PR!