Support Cross Cluster Search

[jbaiera]

Today ES-Hadoop does not support reading data via Elasticsearch's Cross Cluster Search feature.

ES-Hadoop relies on a setup process that needs access to index mappings and general information about the index. Most of these endpoints (like mappings or index health/settings) are not supported for remote indices.

In the future, perhaps we could simplify the setup process to allow for consuming these resources, but until then we should clearly note that remote indices are not supported.