Automate work item assignment with GitLab Duo

Introduces the 'Work item created' trigger for the GitLab Duo Agent Platform, enabling event-driven flows that fire automatically upon work item creation. Details a two-agent flow that uses GitLab Orbit to determine resource workload and assign new work items to the least loaded individual. Provides a step-by-step tutorial demonstrating the trigger and flow in action. Suggests potential enhancements using Model Context Protocol (MCP) for PTO and calendar integration.