Migrate Sailor to use v2 of the elastic.io REST API

Currently, Sailor makes calles to v1 of the elastic.io REST API which is deprecated.  We should migrate to version 2 of the API.  [Example of code calling v1 of the API.](https://github.com/elasticio/sailor-jvm/blob/master/src/main/java/io/elastic/sailor/impl/ApiClientImpl.java#L34)