[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

该 issue 提到了 FlightClient、FlightService 和 gRPC Server；先追踪 Java 客户端如何处理连接，以及如何在 FlightService 中建立身份验证。确定是否可以在保留身份验证的同时使用多个服务器进行负载均衡；完成的标准是得到有文档记录的具体答案，或一个范围明确的后续工作项。

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