[firebase_remote_config] Upgrade to the Remote Config V2 SDKs

[creativecreatorormaybenot]

The current version of firebase_remote_config does not yet use the V2 SDKs.

https://firebase.googleblog.com/2019/08/remote-config-v2-sdk-update.html

[creativecreatorormaybenot]

There are missing functions:

Another important update for smarter fetching is the introduction of the new FetchTimeoutInSeconds and MinimumFetchIntervalInSeconds parameters, which can be used together to provide smarter fetching policies for your app.

[naiduasn]

Any update on when will this be picked up?

[Salakar]

As far as I know we're using the latest Firebase SDKs already, was there something in particular that needs doing? If so please raise a feature request here: https://github.com/FirebaseExtended/flutterfire/discussions/category_choices