Set up a cron job to regularly process osTicket's background jobs

[GabrielMajeri]

Due to the way PHP works, osTicket cannot regularly run background jobs at a specified time interval unless there is some HTTP request happening in this time period.

One solution described in the official documentation is to set up a cron job to regularly poll the /api/cron.php route, which will take care of processing the background tasks.

Since we package up and deploy our osTicket instances as Docker containers, it shouldn't be very hard to modify the Docker images and set up this functionality.