Extract parser setup to helper function

- Allows users who `import` the scripts to examine the parser programmatically

train_db.py

@@ -381,7 +381,7 @@ def train(args):
         print("model saved.")
 
 
-if __name__ == "__main__":
+def setup_parser() -> argparse.ArgumentParser:
     parser = argparse.ArgumentParser()
 
     train_util.add_sd_models_arguments(parser)
@@ -403,6 +403,12 @@ if __name__ == "__main__":
         help="steps to stop text encoder training, -1 for no training / Text Encoderの学習を止めるステップ数、-1で最初から学習しない",
     )
 
+    return parser
+
+
+if __name__ == "__main__":
+    parser = setup_parser()
+
     args = parser.parse_args()
     args = train_util.read_config_from_file(args, parser)