FR: Firebase Storage exponential backoff support

### [READ] Guidelines

I'm building an app that uses Firebase Storage and every now and then I see a 503 Server error, telling me to back off.
I understand that I could take significant time to understand & build truncated exponential backoff for my Storage tasks per https://cloud.google.com/storage/docs/exponential-backoff, but I think it would be better if this was a feature that was available in the SDK, perhaps even on by default (and developers could opt-out etc).
As I understand it, getting backoff to work well (and the tests required) is not trivial. There's a good chance i'd mess it up.