feat: move model loader functionality to augmentation

[willmj]

Description
Step 1 of 3 for enabling LoRA on ScatterMoE: move model loader functionality to augmentation. This makes it so the plugin doesn't have to be standalone as well.

Testing
Testing on fms-hf-tuning with augmentation function instead of model loader shows similar results to #390:

      {
          "model_name_or_path": "/ibm_dmf_lakehouse/models/base_training/shared/granite-3.0-3b-a800m-base/r240924a",
          "training_data_path": "/testing/tuning/input/cc_tone_sft_format_1000_train.json",
          "output_dir": "/testing/tuning/output/granite-3b-moe/ft/20240107_1014-tone-FAST",
          "save_model_dir": "/testing/tuning/output/granite-3b-moe/ft/20240107_1014-tone-FAST/save_model",
          "num_train_epochs": 10.0,
          "per_device_train_batch_size": 2,
          "gradient_accumulation_steps": 1,
          "learning_rate": 1e-5,
          "response_template": "\n### Response:",
          "dataset_text_field": "output",
          "fast_moe": 1
      }

Results:

{'loss': 0.834, 'grad_norm': 326.0, 'learning_rate': 9e-06, 'epoch': 1.0}
{'loss': 0.4279, 'grad_norm': 0.076171875, 'learning_rate': 8.000000000000001e-06, 'epoch': 2.0}
{'loss': 0.1377, 'grad_norm': 3.78125, 'learning_rate': 7e-06, 'epoch': 3.0}
{'loss': 0.0384, 'grad_norm': 0.81640625, 'learning_rate': 6e-06, 'epoch': 4.0}
{'loss': 0.0031, 'grad_norm': 0.003997802734375, 'learning_rate': 5e-06, 'epoch': 5.0}
{'loss': 0.0006, 'grad_norm': 0.002044677734375, 'learning_rate': 4.000000000000001e-06, 'epoch': 6.0}
{'loss': 0.0002, 'grad_norm': 0.0032196044921875, 'learning_rate': 3e-06, 'epoch': 7.0}
{'loss': 0.0001, 'grad_norm': 0.002288818359375, 'learning_rate': 2.0000000000000003e-06, 'epoch': 8.0}
{'loss': 0.0001, 'grad_norm': 0.0087890625, 'learning_rate': 1.0000000000000002e-06, 'epoch': 9.0}
{'loss': 0.0001, 'grad_norm': 0.0115966796875, 'learning_rate': 0.0, 'epoch': 10.0}
{'train_runtime': 2125.7018, 'train_samples_per_second': 4.704, 'train_steps_per_second': 2.352, 'train_loss': 0.14420232288464904, 'epoch': 10.0}                                                                                           

model location: /testing/tuning/output/granite-3b-moe/ft/20240107_1014-tone/save_model

[fabianlim]

I would say add a check for the prescence of name_or_path in model.config, and if not there, raise a ValueError explaining that for scattermoe, we require a name_or_path to point to the model in the config