do not use $lookup for query with variables if only single variable set#147

hallettj wants to merge 10 commits intov1hasura/ndc-mongodb:v1from

jessehallett/eng-1621-mongodb-native-query-cannot-be-used-as-target-of-remote-joinhasura/ndc-mongodb:jessehallett/eng-1621-mongodb-native-query-cannot-be-used-as-target-of-remote-joinCopy head branch name to clipboard