feat: allow artifacts_path to be defined as ENV (#940)

* allow the artifacts_path to be defined as ENV

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

* add check if artifacts_path exists and is dir

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

---------

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

docling/datamodel/settings.py

@@ -1,6 +1,6 @@
 import sys
 from pathlib import Path
-from typing import Annotated, Tuple
+from typing import Annotated, Optional, Tuple
 
 from pydantic import BaseModel, PlainValidator
 from pydantic_settings import BaseSettings, SettingsConfigDict
@@ -62,6 +62,7 @@ class AppSettings(BaseSettings):
     debug: DebugSettings
 
     cache_dir: Path = Path.home() / ".cache" / "docling"
+    artifacts_path: Optional[Path] = None
 
 
 settings = AppSettings(perf=BatchConcurrencySettings(), debug=DebugSettings())