Add support for workflow triggers to determine start node:
- Modified execution_order.py to accept optional start_node_id from triggers
- Updated N8NExecutor to use triggers for determining workflow entry point
- Added helper function to find start node from enabled manual triggers
- Created comprehensive tests for trigger-based execution
- Maintains backward compatibility when no triggers are specified
Co-authored-by: johndoe6345789 <224850594+johndoe6345789@users.noreply.github.com>
