🔧 chore(settings.py): make database_url optional to handle cases where it is not provided

The `database_url` setting is now declared as an optional string (`Optional[str]`) instead of a required string. This change allows the application to handle cases where the `database_url` is not provided, providing more flexibility in the configuration.

src/backend/langflow/settings.py

@@ -1,4 +1,5 @@
 import os
+from typing import Optional
 
 import yaml
 from pydantic import BaseSettings, root_validator
@@ -21,7 +22,7 @@ class Settings(BaseSettings):
     textsplitters: dict = {}
     utilities: dict = {}
     dev: bool = False
-    database_url: str
+    database_url: Optional[str] = None
     cache: str = "InMemoryCache"
     remove_api_keys: bool = False