[Java][Flight] How can a FlightClient connect to multiple servers?

### Describe the usage question you have. Please include as many useful details as possible.

Our backend service is a cluster that allows clients to connect to any service. How does a FlightClient connect to multiple servers and maintain the authentication status. Our goal is load balancing. The server uses FlightService and grpc Server, but the authentication is in FlightService. I don't know how to maintain the authentication status of multiple servers in one FlightClient.

### Component(s)

Java

該 issue 提到了 FlightClient、FlightService 和 gRPC Server；先追蹤 Java 用戶端如何處理連線，以及如何在 FlightService 中建立驗證。確認是否可以在保留驗證的同時使用多個伺服器進行負載平衡；完成的標準是得到有文件記錄的具體答案，或一個範圍明確的後續工作項目。

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