Provide support for loadBalanceHosts connection property

PgJDBC supports [connection load balancing and fail-over](https://jdbc.postgresql.org/documentation/head/connect.html#connection-failover) by accepting a comma-separated list of hosts in the connection string. These hosts are then chosen from serially, or randomly if the `loadBalanceHosts` property is included in the connection string. New connections can be established if any single host is unavailable, giving the appearance of high-availability to the application.

With this library, the host is just "google" and instances are passed through the non-standard `cloudSqlInstance` property. How can I ensure load balancing and high-availability using this library?