Fix json loader - it should go in 'validators' not 'utils'

Fixes #214

src/auto_archiver/core/validators.py

@@ -1,6 +1,7 @@
 # used as validators for config values. Should raise an exception if the value is invalid.
 from pathlib import Path
 import argparse
+import json
 
 def example_validator(value):
     if "example" not in value:
@@ -16,4 +17,7 @@ def positive_number(value):
 def valid_file(value):
     if not Path(value).is_file():
         raise argparse.ArgumentTypeError(f"File '{value}' does not exist.")
-    return value
+    return value
+
+def json_loader(cli_val):
+    return json.loads(cli_val)