[Training] Deprecate Training Surpport (#1882)

SUMMARY:
- Will give the user a warning if `train` is called

Example:

```python
/home/dsikka/llm-compressor/examples/quantization_2of4_sparse_w4a16/llama7b_sparse_w4a16.py:83: DeprecationWarning: Training support will be removed in future releases. Please use the llmcompressor Axolotl integration for fine-tuning https://developers.redhat.com/articles/2025/06/17/axolotl-meets-llm-compressor-fast-sparse-open 
  train(
```

Author: dsikka

src/llmcompressor/entrypoints/train.py

@@ -10,6 +10,7 @@
 import math
 import os
 
+from compressed_tensors.utils import deprecated
 from loguru import logger
 from transformers import PreTrainedModel
 
@@ -22,6 +23,13 @@
 from .utils import post_process, pre_process
 
 
+@deprecated(
+    message=(
+        "Training support will be removed in future releases. Please use "
+        "the llmcompressor Axolotl integration for fine-tuning "
+        "https://developers.redhat.com/articles/2025/06/17/axolotl-meets-llm-compressor-fast-sparse-open"  # noqa: E501
+    )
+)
 def train(**kwargs) -> PreTrainedModel:
     """
     Fine-tuning entrypoint that supports vanilla fine-tuning and