[FR] Connect to Firebase Emulator (Auth) using custom hostname and port

**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()`

首先跟踪 FirebaseAuth 和 FirebaseApp 的初始化，然后对比现有的 FirestoreOptions.setEmulatorHost() 方案。当 FirebaseAuth.getInstance(firebaseApp()).useEmulator('localhost', '9099') 接受用于模拟器连接的自定义主机名和端口（包括动态分配的 TestContainers 端点）时，这项工作就完成了。

由索引模型根据 Issue 内容生成。