checkpoint model on first step callback (#2906)

* checkpoint model on first step callback

* remove debug

* add test cases; update existing tests not to save on first step

* move test out of solo

* delete

* default to False

* typo

tests/e2e/test_embeddings_lr.py

@@ -48,6 +48,7 @@ class TestEmbeddingsLrScale(unittest.TestCase):
                 "save_safetensors": True,
                 "bf16": "auto",
                 "use_tensorboard": True,
+                "save_first_step": False,
             }
         )
 
@@ -93,6 +94,7 @@ class TestEmbeddingsLrScale(unittest.TestCase):
                 "save_safetensors": True,
                 "bf16": "auto",
                 "use_tensorboard": True,
+                "save_first_step": False,
             }
         )
         cfg = validate_config(cfg)