Choosing Whether to Enable Retries in Firebase App Options

Hello,
I have learned that FCM automatically retries when a 503 response is received.
However, our service already handles retries for undelivered messages through scheduling, so we do not want to use the default retry strategy.
```
public static HttpRequestFactory newAuthorizedRequestFactory(
FirebaseApp app, @Nullable RetryConfig retryConfig) {
HttpTransport transport = app.getOptions().getHttpTransport();
return transport.createRequestFactory(new FirebaseRequestInitializer(app, retryConfig));
}
```
To disable this behavior, I attempted to use a method provided in the ApiClientUtils class.
However, after debugging the initialization process, I found that it is not possible to set a custom RetryConfig value.

I assume there is a valid reason for restricting the redefinition of RetryConfig.
For example, it may be to prevent retries for responses other than 5xx errors or to avoid excessive retry requests within a short period.

What I would like is the ability to **enable or disable the retry feature as needed.**
I will proceed with creating a PR for this.

首先，追蹤 ApiClientUtils 與所示的 newAuthorizedRequestFactory 方法在 FirebaseApp 初始化過程中的呼叫路徑，重點確定 RetryConfig 在哪裡被固定或限制。確定一種受支援的方式來啟用或停用重試，同時不改變無關的重試行為，並驗證兩種設定模式都適用於 FCM 請求。

由索引模型根據 Issue 內容生成。