[6.x] Allow easier customization of the queued mailable job (#31684)

* Allow easier customization of the queued mailable job.

This will allow developers to override this makeQueuedJob method in their mailables and return their own job - which means we can enable job middlewares rate limiting etc easily for all mailables.

* Update Mailable.php

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

Author: garygreen

src/Illuminate/Mail/Mailable.php

@@ -177,7 +177,7 @@ public function queue(Queue $queue)
         $queueName = property_exists($this, 'queue') ? $this->queue : null;
 
         return $queue->connection($connection)->pushOn(
-            $queueName ?: null, new SendQueuedMailable($this)
+            $queueName ?: null, $this->newQueuedJob()
         );
     }
 
@@ -195,10 +195,20 @@ public function later($delay, Queue $queue)
         $queueName = property_exists($this, 'queue') ? $this->queue : null;
 
         return $queue->connection($connection)->laterOn(
-            $queueName ?: null, $delay, new SendQueuedMailable($this)
+            $queueName ?: null, $delay, $this->newQueuedJob()
         );
     }
 
+    /**
+     * Make the queued mailable job instance.
+     *
+     * @return mixed
+     */
+    protected function newQueuedJob()
+    {
+        return new SendQueuedMailable($this);
+    }
+
     /**
      * Render the mailable into a view.
      *