add_comfyui_save_graph_dir_variable (#673)

需求来源：李倞，需要将图保存到指定目录。

onediff_comfy_nodes/utils/graph_path.py

@@ -1,4 +1,5 @@
 import hashlib
+import os
 from pathlib import Path
 from oneflow import __version__ as oneflow_version
 
@@ -14,7 +15,10 @@ def generate_short_sha256(string: str) -> str:
 
 
 def generate_graph_path(ckpt_name, model) -> Path:
-    input_dir = get_input_directory()
+    # get_save_graph_directory
+    default_dir = get_input_directory()
+    input_dir = os.getenv("COMFYUI_ONEDIFF_SAVE_GRAPH_DIR", default_dir)
+
     input_dir = Path(input_dir)
     graph_dir = input_dir / "graphs" / ckpt_name