Is your feature request related to a problem? Please describe.
I am trying to setup a testing phase that would run tests on the Emulator by connecting to it. The Emulator is prepared using TestContainers which don't open specific ports, but rather random. Because of this I cannot use the environment variable specified as that blocks me into selecting a hostname and port.

Describe the solution you'd like
Make the hostname and port dynamic when initialising FirebaseAuth / FirebaseApp.

Describe alternatives you've considered

Additional context

Expected usage

FirebaseAuth.getInstance(firebaseApp()).useEmulator('localhost', '9099')

For example, Firestore has this enabled using FirestoreOptions.newBuilder().setEmulatorHost()