[{"_id":ObjectId("5e940d6c2f804ab99b24a633"),"accountId":ObjectId("7e1c1180d59de1704ce43557"),"description":"some desc","configs":{},"dependencies":[{"commute":{},"distance":{},"support":{}},{"commute2":{},"distance2":{},"support2":{}}]}]

db.collection.aggregate([{$project:{_id:0,dependenciesKeys:{$reduce:{input:"$dependencies",initialValue:[],in:{$concatArrays:["$$value",{$map:{input:{$objectToArray:"$$this"},in:"$$this.k"}}]}}}}}])