add type hint in pipeline model argument
# What does this PR do?

This PR adds type hints for model argument in pipeline function

## Who can review?
@Narsil 
@amyeroberts 

_The documentation is not available anymore as the PR was closed or merged._<|||||>I think I should add PretrainedModel and TFPretrainedModel in string form just like PreTrainedTokenizerFast was given in tokenizer argument. TYPE_CHECKING is false by default<|||||>LGTM.
