Moved all model names into an enum

aider/utils.py

@@ -1,11 +1,17 @@
 import math
 import re
 from difflib import SequenceMatcher
+from enum import Enum
 from pathlib import Path
 
 # from aider.dump import dump
 
 
+class Models(Enum):
+    GPT4 = "gpt-4"
+    GPT35 = "gpt-3.5-turbo"
+
+
 def try_dotdotdots(whole, part, replace):
     """
     See if the edit block has ... lines.