Add total votes to consensus reducer output

[lcjohnso]

It is common for project teams to write a retirement rule based on consensus reducer outputs where the conditions are:

• for a certain answer (["eq", ["lookup", "consensus.most_likely", ""], ["const", "2"]])
• subject agreement higher than some threshold (["gte", ["lookup", "consensus.agreement", 0], ["const", 0.8]])
• total classifications greater than some threshold (["gte", ["lookup", "count.classifications", 0], ["const", 10]])

It is annoying that a second reducer is required to track the total classification count, when the consensus reducer computes that value internally (as part of the agreement calculation: num_votes / total_votes).

Furthermore: the num_votes metric, which represents the number of classifications tallied for the most_likely answer, is frequently mistaken for the total number of votes during configuration.

This PR adds a total_votes key to the consensus reducer data output for convenience.