Allow a way to leverage flavors in order to use multiple firebase environments.

[ochmist]

Hello,

We are trying to implement ci/cd for our web app but we are struggling with automating deployment since we have not found a good way to load firebaseConfig dynamically depending on which environment we are running in.

It is already pretty well documented on how to do the same thing for Android and iOS, and the same functionality would be greatly appreciated for web.

Thanks!