Add Gold Rush to Solr Documents.

[kevinreiss]

User story

As a system that wants to match identical records I would like a key in each solr document that creates a string value I can use to compare to group matches.

Acceptance criteria

• If this change touches any of the files referenced in .rubocop_todo.yml create a new ticket to address the rubocop todo.
• We add code that will calculate a gold rush key for each marc record
• The key is a stored field in each solr document.
• We should note the impact of the addition of this key to the size of the index and any differences noted in processing time for MARC records.

The Gold rush algorithm to use to calculate should be the one that results from this ticket.