feat(aggregate): support hit field for aggregate command

Supports passing an index hint to the aggregate command

Author: daprahamian

lib/collection.js

@@ -2460,6 +2460,7 @@ Collection.prototype.aggregate = function(pipeline, options, callback) {
         opts.cursor ||
         opts.out ||
         opts.maxTimeMS ||
+        opts.hint ||
         opts.allowDiskUse)
         ? args.pop()
         : {};
@@ -2504,6 +2505,9 @@ Collection.prototype.aggregate = function(pipeline, options, callback) {
   if (options.allowDiskUse) command.allowDiskUse = options.allowDiskUse;
   if (typeof options.maxTimeMS === 'number') command.maxTimeMS = options.maxTimeMS;
 
+  // If we are giving a hint
+  if (options.hint) command.hint = options.hint;
+
   options = shallowClone(options);
   // Ensure we have the right read preference inheritance
   options = getReadPreference(this, options, this.s.db, this);