fix: Enabled automatic HTTP retries for FirebaseProjectManagement

[hiranya911]

Enables automatic HTTP retries for the FirebaseProjectManagement API. We disable retries for unit tests for faster execution of tests.

RELEASE NOTE: Project management APIs in the FirebaseProjectManagement class now automatically retries operations that fail due to retry-eligible HTTP errors.

[weixifan]

At first I kind of want to say we should bake this assertion into the API infrastructure itself instead of directly verifying in a unit test that no one touched the code. But then the OO design I came up with to facilitate this turns out to be impossible due to various classes being final. I was hoping that we can write a subclass of HttpRequest called RetryingHttpRequest that declares at compile time that getUnsuccessfulResponseHandler will return RetryHandlerDecorator or a suitable base class, but alas, HttpRequest is final. (And so is HttpRequestFactory, which is the other class I wanted to subclass.)

Without the above OO structure, the only other way to structure the test to be more behavioural would be to treat the retrying mechanism completely like a black box, and empirically measure retry intervals and retry counts after forcing an unsuccessful response. This is going to be painfully flaky, so I think what you have is probably for the best.

[weixifan]

Overall LGTM. The only comment I left is just an interesting observation.