add download command

lama_cleaner/download.py

@@ -0,0 +1,24 @@
+import os
+
+from loguru import logger
+from pathlib import Path
+
+
+def cli_download_model(model: str, model_dir: str):
+    if os.path.isfile(model_dir):
+        raise ValueError(f"invalid --model-dir: {model_dir} is a file")
+
+    if not os.path.exists(model_dir):
+        logger.info(f"Create model cache directory: {model_dir}")
+        Path(model_dir).mkdir(exist_ok=True, parents=True)
+
+    os.environ["XDG_CACHE_HOME"] = model_dir
+
+    from lama_cleaner.model_manager import models
+
+    if model in models:
+        logger.info(f"Downloading {model}...")
+        models[model].download()
+        logger.info(f"Done.")
+    else:
+        logger.info(f"Downloading model from Huggingface: {model}")