Add background driver (laravel#6699)

* Add background driver

Adds settings for PR laravel/framework#57648

* Update queue.php

---------

Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: barryvdh

config/queue.php

@@ -25,7 +25,7 @@
     | each backend supported by Laravel. You're also free to add more.
     |
     | Drivers: "sync", "database", "beanstalkd", "sqs", "redis",
-    |          "deferred", "failover", "null"
+    |          "deferred", "background", "failover", "null"
     |
     */
 
@@ -77,6 +77,10 @@
             'driver' => 'deferred',
         ],
 
+        'background' => [
+            'driver' => 'background',
+        ],
+
         'failover' => [
             'driver' => 'failover',
             'connections' => [