Fix reloading of the transformer-based models

[sararb]

Fixes #1132

Goals :soccer:

• Import transformers assets when the Hugging Face library is installed.

Implementation Details :construction:

• Add import transformers in the init file of Merlin Models

Testing Details :mag:

• The issue is happening when we try to reload a model in a different python process to the one that saved the model.

[github-actions[bot]]

Documentation preview

https://nvidia-merlin.github.io/models/review/pr-1147