Adds use_auth_token with pipelines
# What does this PR do?

This PR adds `use_auth_token` as a named parameter to the `pipeline`. Also fixed `AutoConfig.from_pretrained` adding the `model_kwargs` as `**kwargs` to load private model with `use_auth_token`. 

**Possible Usage for `pipeline` with `use_auth_token`:**
with model_kwargs
```python
hf_pipeline = pipeline('sentiment-analysis',
                       model='philschmid/sagemaker-getting-started',
                       tokenizer='philschmid/sagemaker-getting-started',
                       model_kwargs={"use_auth_token": "xxx"})
```
as named paramter
```python
hf_pipeline = pipeline('sentiment-analysis',
                       model='philschmid/sagemaker-getting-started',
                       tokenizer='philschmid/sagemaker-getting-started',
                       use_auth_token = "xxx")
```

cc @Narsil 