[Java][Flight] Add caching of FlightClients to JDBC

### Describe the enhancement requested

When getFlightInfo reports a list of endpoints, the driver internally creates a FlightClient for each endpoint that reports a Location. These clients can benefit from being cached/pooled since a server will likely re-use endpoints for subsequent queries. This should likely be a configuration option.

The driver should also check if the Location at an endpoint is the same as the original location used when calling getFlightInfo and avoid creating a new FlightClient in this case.

Investigate using https://github.com/ben-manes/caffeine for caching.

### Component(s)

FlightRPC, Java

Start by tracing the Java JDBC driver's getFlightInfo path and how it creates FlightClients for returned Locations. Investigate Caffeine as suggested, then define a configuration option for client caching or pooling and verify that the original Location is reused without creating a duplicate client. Done means endpoint clients are reused for subsequent queries while the original location avoids an extra client.

Written by the indexing model from the issue text.