Please add support for OpenTracing

[AceHack]

Here is a sync solr client with open tracing
https://github.com/opentracing-contrib/java-solr-client

More info on open tracing
https://opentracing.io/

Here is a tracing issue on solr
https://issues.apache.org/jira/browse/SOLR-13434

[magro]

A PR for this would be awesome! 😊

[magro]

Note2self - related Solr PR: apache/lucene-solr#685