feat(api): Human Input Node (backend part) (#31646)

The backend part of the human in the loop (HITL) feature and relevant architecture / workflow engine changes.

Signed-off-by: yihong0618 <zouzou0208@gmail.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: -LAN- <laipz8200@outlook.com>
Co-authored-by: 盐粒 Yanli <yanli@dify.ai>
Co-authored-by: CrabSAMA <40541269+CrabSAMA@users.noreply.github.com>
Co-authored-by: Stephen Zhou <38493346+hyoban@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: yihong <zouzou0208@gmail.com>
Co-authored-by: Joel <iamjoel007@gmail.com>

api/models/__init__.py

@@ -34,6 +34,8 @@ from .enums import (
     WorkflowRunTriggeredFrom,
     WorkflowTriggerStatus,
 )
+from .execution_extra_content import ExecutionExtraContent, HumanInputContent
+from .human_input import HumanInputForm
 from .model import (
     AccountTrialAppRecord,
     ApiRequest,
@@ -155,9 +157,12 @@ __all__ = [
     "DocumentSegment",
     "Embedding",
     "EndUser",
+    "ExecutionExtraContent",
     "ExporleBanner",
     "ExternalKnowledgeApis",
     "ExternalKnowledgeBindings",
+    "HumanInputContent",
+    "HumanInputForm",
     "IconType",
     "InstalledApp",
     "InvitationCode",