[FT] Allow configuration of `litellm` cache location

## Issue encountered

In `lighteval==0.10.0`, the creation of `litellm`'s `Cache`: https://github.com/huggingface/lighteval/blob/v0.10.0/src/lighteval/models/litellm_model.py#L59

Does not allow for configuration of the cache location.

## Solution/Feature

Allow configuration of the cache location via an environment variable like so:

```python
LIGHTEVAL_LITELLM_CACHE_LOCATION = os.environ.get("LIGHTEVAL_LITELLM_CACHE_LOCATION")

litellm.cache = Cache(type="disk", disk_cache_dir=LIGHTEVAL_LITELLM_CACHE_LOCATION)
```

## Possible alternatives

N/a