Change type msg_location to an Enum instead of Literal to be able to get all values easy and improve type checks.

tests/test_hist_cmd.py

@@ -4,7 +4,7 @@ import tempfile
 import yaml
 from pathlib import Path
 from chatmastermind.message import Message, Question
-from chatmastermind.chat import ChatDB, ChatError
+from chatmastermind.chat import ChatDB, ChatError, msg_location
 from chatmastermind.configuration import Config
 from chatmastermind.commands.hist import convert_messages
 
@@ -41,7 +41,7 @@ class TestConvertMessages(unittest.TestCase):
     def test_convert_messages(self) -> None:
         self.args.convert = 'yaml'
         convert_messages(self.args, self.config)
-        msgs = self.chat.msg_gather(loc='disk', glob='*.*')
+        msgs = self.chat.msg_gather(loc=msg_location.DISK, glob='*.*')
         # Check if the number of messages is the same as before
         self.assertEqual(len(msgs), len(self.messages))
         # Check if all messages have the requested suffix