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/core/app/entities/app_invoke_entities.py

@@ -17,9 +17,24 @@ class InvokeFrom(Enum):
     Invoke From.
     """
 
+    # SERVICE_API indicates that this invocation is from an API call to Dify app.
+    #
+    # Description of service api in Dify docs:
+    # https://docs.dify.ai/en/guides/application-publishing/developing-with-apis
     SERVICE_API = "service-api"
+
+    # WEB_APP indicates that this invocation is from
+    # the web app of the workflow (or chatflow).
+    #
+    # Description of web app in Dify docs:
+    # https://docs.dify.ai/en/guides/application-publishing/launch-your-webapp-quickly/README
     WEB_APP = "web-app"
+
+    # EXPLORE indicates that this invocation is from
+    # the workflow (or chatflow) explore page.
     EXPLORE = "explore"
+    # DEBUGGER indicates that this invocation is from
+    # the workflow (or chatflow) edit page.
     DEBUGGER = "debugger"
 
     @classmethod