Add cron scheduling support for automated workflow triggers

Summary

Add the ability to schedule workflow execution based on cron expressions. This enables automated, time-based workflow execution without requiring manual intervention or external scheduling tools.

Business Value

• Enables scheduled report generation, data synchronization, and maintenance tasks
• Reduces dependency on external cron management tools
• Provides a familiar cron expression syntax for scheduling
• Integrates with Drupal's existing cron infrastructure

Features Implemented

• Cron event type added to the trigger system
• Cron schedule configuration UI in trigger forms
• Support for standard cron expression syntax
• Drush commands for manual trigger testing

Use Cases

• Daily data cleanup workflows
• Scheduled content publishing pipelines
• Periodic API synchronization tasks
• Automated backup and maintenance routines