feat(permissions): add per-group features.user_webhooks permission (#25923)

backend/open_webui/routers/users.py

@@ -239,6 +239,7 @@ class FeaturesPermissions(BaseModel):
     memories: bool = True
     automations: bool = False
     calendar: bool = True
+    user_webhooks: bool = False
 
 
 class SettingsPermissions(BaseModel):