Adding functionality for offline loading

[shubham-s-agarwal]

This change modifies the BERT model loading logic to support offline initialization from local files only, removing any dependency on online resources.

New behavior:

• If load_bert_pretrained_weights=True: load pretrained BERT weights (requires internet access).
• If load_bert_pretrained_weights=False: initialize BERT with random weights

Note: we always recommend loading the model weights from the provided model packs. In case user does not want to load the model pack, then using load_bert_pretrained_weights=False is unadvisable, however in our scripts, we always load the model packs.

• If saved_dir_path is provided:
  • Load BERT config from local file in the specified path.
• If saved_dir_path is not provided:
  • Fallback to downloading config from HuggingFace.