Allow for environment variable to set NNI configuration directory (#3936)

Co-authored-by: Mark Janse <m.h.a.janse-2@umcutrecht.nl>

nni/runtime/config.py

@@ -13,7 +13,9 @@ def get_config_directory() -> Path:
     Get NNI config directory.
     Create it if not exist.
     """
-    if sys.prefix != sys.base_prefix or Path(sys.prefix, 'conda-meta').is_dir():
+    if os.getenv('NNI_CONFIG_DIR') is not None:
+        config_dir = Path(os.getenv('NNI_CONFIG_DIR'))
+    elif sys.prefix != sys.base_prefix or Path(sys.prefix, 'conda-meta').is_dir():
         config_dir = Path(sys.prefix, 'nni')
     elif sys.platform == 'win32':
         config_dir = Path(os.environ['APPDATA'], 'nni')