Implement endpoint for the Geo Analytics service.

• editors/by-country endpoint is implemented

Note: the existing production AQS service exposes a number of editors/ endoints. Most of these are Druid-based and, for the purposes of AQS 2.0, are being considered part of the "Editor Analytics". The editors/by-country endpoint is Cassandra-based and is the sole endpoint provided by the "Geo Analytics service".