Add queue worker for fire-and-forget workflow execution

Summary

Add a queue worker that processes fire-and-forget workflow executions. This enables truly asynchronous workflow execution where the parent workflow doesn't wait or track the child workflow's completion.

Business Value

• Enables non-blocking workflow spawning for background tasks
• Leverages Drupal's queue system for reliable execution
• Supports high-throughput scenarios by deferring work to cron
• Prevents parent workflow timeout when spawning long-running tasks

Technical Implementation

• Queue name: workflow_executor_queue
• Cron time allocation: 120 seconds per run
• Creates playground session for each queued workflow
• Triggers workflow execution via PlaygroundService
• Preserves parent context for recursion tracking

Queue Item Structure

• workflow_id: The workflow to execute
• input_data: Input data for the workflow
• parent_context: Execution depth and workflow chain for safety

Use Cases

• Send notifications without blocking the main workflow
• Spawn cleanup tasks after primary processing completes
• Trigger downstream workflows in event-driven architectures
• Batch spawn multiple independent workflows