feat: user webhooks system settings

backend/open_webui/config.py

@@ -1092,6 +1092,12 @@ ENABLE_MESSAGE_RATING = PersistentConfig(
     os.environ.get("ENABLE_MESSAGE_RATING", "True").lower() == "true",
 )
 
+ENABLE_USER_WEBHOOKS = PersistentConfig(
+    "ENABLE_USER_WEBHOOKS",
+    "ui.enable_user_webhooks",
+    os.environ.get("ENABLE_USER_WEBHOOKS", "True").lower() == "true",
+)
+
 
 def validate_cors_origins(origins):
     for origin in origins: