Add combined index

With multiple queues and thousands of messages, MongoDB is doing a full collection scan.

The combined index solves that.

Author: ddziaduch

MongodbContext.php

@@ -161,5 +161,6 @@ public function createCollection(): void
         $collection->createIndex(['queue' => 1], ['name' => 'enqueue_queue']);
         $collection->createIndex(['priority' => -1, 'published_at' => 1], ['name' => 'enqueue_priority']);
         $collection->createIndex(['delayed_until' => 1], ['name' => 'enqueue_delayed']);
+        $collection->createIndex(['queue' => 1, 'priority' => -1, 'published_at' => 1, 'delayed_until' => 1], ['name' => 'enqueue_combined']);
     }
 }