feat(aggregate): add Aggregate#search() for Atlas Text Search

Fix #9115

lib/aggregate.js

@@ -909,6 +909,32 @@ Aggregate.prototype.facet = function(options) {
   return this.append({ $facet: options });
 };
 
+/**
+ * Helper for [Atlas Text Search](https://docs.atlas.mongodb.com/reference/atlas-search/tutorial/)'s
+ * `$search` stage.
+ *
+ * ####Example:
+ *
+ *     Model.aggregate().
+ *      search({
+ *        text: {
+ *          query: 'baseball',
+ *          path: 'plot'
+ *        }
+ *      });
+ *
+ *     // Output: [{ plot: '...', title: '...' }]
+ *
+ * @param {Object} $search options
+ * @return {Aggregate} this
+ * @see $search https://docs.atlas.mongodb.com/reference/atlas-search/tutorial/
+ * @api public
+ */
+
+Aggregate.prototype.search = function(options) {
+  return this.append({ $search: options });
+};
+
 /**
  * Returns the current pipeline
  *