llama_or_mistral_ckpt.py file requiring checkpoints in local file system

[shivajid]

The llama_or_mistral_ckpt.py requires --base-model-path to be in local file system, whereas the --maxtext-model-path is GCS. It would be good to change the implmentation to use fsspec or tf GFile or some universal file reader that can read file from gcs and local filepath.