feat(trigger): enhance trigger debugging with polling API and new subscription retrieval

- Refactored DraftWorkflowTriggerNodeApi and DraftWorkflowTriggerRunApi to implement polling for trigger events instead of listening, improving responsiveness and reliability.
- Introduced TriggerSubscriptionBuilderGetApi to retrieve subscription instances for trigger providers, enhancing the API's capabilities.
- Removed deprecated trigger event classes and streamlined event handling in TriggerDebugService, ensuring a cleaner architecture.
- Updated Queue and Stream entities to reflect the changes in trigger event handling, improving overall clarity and maintainability.

These enhancements significantly improve the trigger debugging experience and API usability.

api/services/workflow_service.py

@@ -347,7 +347,7 @@ class WorkflowService:
         node_config = draft_workflow.get_node_config_by_id(node_id)
         node_type = Workflow.get_node_type_from_node_config(node_config)
         node_data = node_config.get("data", {})
-        if node_type == NodeType.START:
+        if node_type.is_start_node:
             with Session(bind=db.engine) as session, session.begin():
                 draft_var_srv = WorkflowDraftVariableService(session)
                 conversation_id = draft_var_srv.get_or_create_conversation(