Add deprecation notice to /spend/logs endpoint

- Mark /spend/logs as deprecated in docstring
- Direct users to use /spend/logs/v2 for paginated access
- Warns about performance issues with non-paginated endpoint

Author: AlexsanderHamir

litellm/proxy/spend_tracking/spend_management_endpoints.py

@@ -1917,6 +1917,9 @@ async def view_spend_logs(  # noqa: PLR0915
     user_api_key_dict: UserAPIKeyAuth = Depends(user_api_key_auth),
 ):
     """
+    [DEPRECATED] This endpoint is not paginated and can cause performance issues.
+    Please use `/spend/logs/v2` instead for paginated access to spend logs.
+
     View all spend logs, if request_id is provided, only logs for that request_id will be returned
 
     When start_date and end_date are provided: