### Check for existing issues

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

### The Feature

We propose to enrich litellm's existing llm call metrics via an optionnal Ecologits plugin that will provide green-cost metrics, based on the [Ecologits API](https://api.ecologits.ai/docs) calculator, and for visibility through all the downstream observability callback plugin: Datadog, Langfuse, etc.

For this first raw 'proxy mode' functional version, the principle is simple:

- when a new model is registered, the litellm admins can add a model info argument untitled "ecologits_electricity_mix_zone" (e.g. 'FRA', 'DEU') for this model. If they do not, the default electrify mix zone call back simply to the default zone "WOR" (for "world").

- for each successfull call from litellm to an llm provider, the green impact is evaluated with an API call to Ecologits API (or the internal Ecologits API self-hosted by the enterprise) and these new green metric enrich the initial payload for all the litellm supported callback integrations plugin, choosen by the users: langfuse, datadog, prometheus metrics ... For this latest, some green-cost metrics counter a…