Add environment variable for per_schedule_task_limit (pterodactyl#3557)

The environment variable `PTERODACTYL_PER_SCHEDULE_TASK_LIMIT` can be used to change the maximum number of tasks per schedule.

Author: TekExplorer

config/pterodactyl.php

@@ -141,7 +141,7 @@
 
         'schedules' => [
             // The total number of tasks that can exist for any given schedule at once.
-            'per_schedule_task_limit' => 10,
+            'per_schedule_task_limit' => env('PTERODACTYL_PER_SCHEDULE_TASK_LIMIT', 10),
         ],
 
         'allocations' => [