Fix cached_path error with transformers v4.22

[davidmezzetti]

Transformers v4.22 removed the cached_path method with huggingface/transformers#18497.

This is resulting in the following error when running with transformers==4.22.0

ImportError: cannot import name 'cached_path' from 'transformers.file_utils'

The translation pipeline needs to be updated with an equivalent way to run cached_path like functionality for files not on the Hugging Face Hub.

The workaround for txtai < 5.0 is to pin transformers to <= 4.21.3.

[davidmezzetti]

This issue also addresses a UserWarning in the translation pipeline regarding setting max_length in the model.generate call.