[FT] Align parameter names in config files and config classes

## Issue encountered
Currently, the example config files have a parameter named `dtype`.

When parsing the config file into the config class, this parameter is renamed to `model_dtype`.

## Solution/Feature
Align the name to `model_dtype` in both config files and config classes.

### Context:
In the config files
- it already exists a `model` parameter called `model_name`
- there are also `instance` parameters called `instance_type` and `instance_size`

This was discussed in:
- https://github.com/huggingface/lighteval/pull/434?new_mergebox=true#issue-2732500452

## Possible alternatives
Leave it as it is.