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

examples/orpheus/finetune.yml

@@ -50,3 +50,5 @@ weight_decay: 0.05
 
 special_tokens:
   pad_token: <custom_token_7>
+
+# save_first_step: true  # uncomment this to validate checkpoint saving works with your config