Support for Aggregate Queries (#4207)

* Support for Aggregate Queries

* improve pg and coverage

* Mongo 3.4 aggregates and tests

* replace _id with objectId

* improve tests for objectId

* project with group query

* typo

src/Adapters/Storage/Mongo/MongoCollection.js

@@ -60,6 +60,14 @@ export default class MongoCollection {
     return countOperation;
   }
 
+  distinct(field, query) {
+    return this._mongoCollection.distinct(field, query);
+  }
+
+  aggregate(pipeline, { maxTimeMS, readPreference } = {}) {
+    return this._mongoCollection.aggregate(pipeline, { maxTimeMS, readPreference }).toArray();
+  }
+
   insertOne(object) {
     return this._mongoCollection.insertOne(object);
   }