unify and optimize count aggregations over grouped and ungrouped data#146

hallettj merged 6 commits intomainhasura/ndc-mongodb:mainfrom

jessehallett/eng-1465-mongodb-make-sure-count-by-distinct-works-correctlyhasura/ndc-mongodb:jessehallett/eng-1465-mongodb-make-sure-count-by-distinct-works-correctlyCopy head branch name to clipboard