[ENG-2740] Revert "Remove <repositories> per section 6 of the Sonatype guide."
[ENG-2740] Revert "Remove <repositories> per section 6 of the Sonatype guide."

This reverts commit 849d9b3ded638bcfb8b79a257f2cbde53a51f6d3.
ElasticSearch's artifacts only seem to exist outside of Central so we
can't build without it.

tmayfield/elasticsearch-jetty,sonian/elasticsearch-jetty,whitefoxx/elasticsearch-jetty,JoeyJiao/elasticsearch-jetty,paul-e-cooley/elasticsearch-jetty,tmayfield/elasticsearch-jetty,JoeyJiao/elasticsearch-jetty,paul-e-cooley/elasticsearch-jetty,sonian/elasticsearch-jetty,whitefoxx/elasticsearch-jetty