Change zk configs to use Jackson injection instead of Skife

In an effort to make configuration more standard across various portions of the Druid modules, things are slowly migrating over to the Jackson configuration bindings instead of using the skife configuration stuff. This is but one portion of that overall migration.
Yes, there's now a IndexerZkConfig and a general ZkPathsConfig. The Indexer config contains an injected instance of the ZkPathsConfig