### Check for existing issues

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

### What happened?

Deleting a non-existent response via the LiteLLM proxy returns HTTP 500 instead of HTTP 404

Expected status code is 404, but actual status code is 500 with response: { "error": { "message": "litellm.APIConnectionError: azure - {\n \"error\": {\n \"message\": \"Response with id 'resp_...' not found.\",\n \"type\": \"invalid_request_error\",\n \"param\": null,\n \"code\": null\n }\n}.", "type": null, "param": null, "code": "500" } }

### Steps to Reproduce

Example request: curl -X 'DELETE' \ 'http://localhost:4000/openai/v1/responses/[nonexist response id]' \ -H 'accept: application/json' \ -H 'x-litellm-api-key: [litellm-admin-key]'

### Relevant log output

```shell { "error": { "message": "litellm.APIConnectionError: azure - {\n \"error\": {\n \"message\": \"Response with id 'resp_...' not found.\",\n \"type\": \"invalid_request_error\",\n \"param\": null,\n \"code\": null\n }\n}.", "type": null, "param": null, "code": "500" } } ```

### Wh…