Default to empty DC failover preferred remoted DCs

[jahstreet]

In https://github.com/apache/cassandra-java-driver/pull/1896 we added a feature to prefer the order of the remote DCs on the x-DC failovers. As described in https://github.com/apache/cassandra-java-driver/pull/1896#discussion_r1983231999, the default is misleading to errors. With this tiny change I propose to default to empty list i/o containing a single empty string value.

cc @nitinitt