Add ability to flatten and expand for object indexing

This patch set introduces the chef_index_expand module that knows how to flatten and expand Chef object JSON into the format expected by solr.

There is test coverage and behavior should be very similar to chef-expander. However, still on the TODO list is a more comprehensive A/B test with chef-expander.

This code is unlikely to be immediately useful, but could help us in re-indexing scenarios as well as exploration of search infra upgrade.