### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

I am using LiteLLM Proxy to route requests to a custom server that simulates the OpenAI Batch/Files API. While `add_user_information_to_llm_headers: true` works perfectly for `/v1/chat/completions` (forwarding user and team metadata), these headers are missing when LiteLLM proxies requests to the `/v1/files` or `/v1/batches` endpoints.

### Configuration ``` model_list: - model_name: mymodel litellm_params: api_base: http://batchserver/v1 model: hosted_vllm/mymodel api_key: change-me

general_settings: add_user_information_to_llm_headers: true ```

Is this a current limitation of the middleware responsible for header forwarding? If so, would it be feasible to extend `add_user_information_to_llm_headers` to cover the File and Batch management endpoints?

### Steps to Reproduce

1. Start the LiteLLM Proxy with the config above. 2. Make a request to /v1/chat/completions using a valid LiteLLM Key. - Result: The backend server receives headers like litellm-user-id or litellm-team-id. (Expected behavior).

3. Make a requ…