feat: Persist Variables for Enhanced Debugging Workflow (#20699)

This pull request introduces a feature aimed at improving the debugging experience during workflow editing. With the addition of variable persistence, the system will automatically retain the output variables from previously executed nodes. These persisted variables can then be reused when debugging subsequent nodes, eliminating the need for repetitive manual input.

By streamlining this aspect of the workflow, the feature minimizes user errors and significantly reduces debugging effort, offering a smoother and more efficient experience.

Key highlights of this change:

- Automatic persistence of output variables for executed nodes.
- Reuse of persisted variables to simplify input steps for nodes requiring them (e.g., `code`, `template`, `variable_assigner`).
- Enhanced debugging experience with reduced friction.

Closes #19735.

api/services/app_dsl_service.py

@@ -32,6 +32,7 @@ from models import Account, App, AppMode
 from models.model import AppModelConfig
 from models.workflow import Workflow
 from services.plugin.dependencies_analysis import DependenciesAnalysisService
+from services.workflow_draft_variable_service import WorkflowDraftVariableService
 from services.workflow_service import WorkflowService
 
 logger = logging.getLogger(__name__)
@@ -292,6 +293,8 @@ class AppDslService:
                 dependencies=check_dependencies_pending_data,
             )
 
+            draft_var_srv = WorkflowDraftVariableService(session=self._session)
+            draft_var_srv.delete_workflow_variables(app_id=app.id)
             return Import(
                 id=import_id,
                 status=status,