### Check for existing issues

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

### What happened?

I set up Vantage integration as described [here](https://github.com/BerriAI/litellm-docs/blob/main/docs/observability/vantage.md). LiteLLM sends the request, but receives 422 error, which means the payload has wrong format.

I tried to upload [dry-run](https://github.com/BerriAI/litellm-docs/blob/main/docs/observability/vantage.md#2-preview-data-dry-run) output as a CSV file via Vantage UI and got the following error: "ServiceName can't be blank".

So I think the problem is that LiteLLM sends to Vantage all the requests, including the ones that are not LLM requests. The field `model_group` (which is translated to `ServiceName` for Vantage) is blank for such requests, and it causes problems.

I see following possible solutions: - filter out all the records that have blank `model_group` (but there still might be some cost, so it's not the best solution) - put some placeholder into `ServiceName` field for the non-LLM requests, so it is not blank for Vantage

### Steps to Reproduce

1. set up Vantage integration 2. make any non-LLM request to LiteL…