Use "count" metricAggregation when no metricColumnY but there is bucketColumn [#1055]
Use "count" metricAggregation when no metricColumnY but there is bucketColumn [#1055]

in `/backend/src/akvo/lumen/lib/aggregation/bar.clj` if we do not send `metricColumnY` in the query parameters but we do send bucketColumn then we need to use count aggregation for the y value. make sense?

akvo/akvo-dash,akvo/akvo-lumen,akvo/akvo-dash,akvo/akvo-lumen,akvo/akvo-dash