Set a LIMIT on the query to avoid processing more than "reasonable" number of orders at the single cron run

Problem/Motivation

If the website is processing thousands of active subscriptions that run on a frequent schedule (ex hourly) we may run into a situation where the cron is not able to process all orders before the process is killed. This may have bad implications for the entire Drupal instance.

To mitigate that issue this module should declare the maximum number of orders that are processed during a single cron run. Said number should be relatively low to allow other modules hooking into hook_cron to execute as well.