Add support for gpt-5

Author: jdormit

gptel-openai.el

@@ -294,7 +294,7 @@ Mutate state INFO with response metadata."
            :messages [,@prompts]
            :stream ,(or gptel-stream :json-false)))
         (reasoning-model-p ; TODO: Embed this capability in the model's properties
-         (memq gptel-model '(o1 o1-preview o1-mini o3-mini o3 o4-mini))))
+         (memq gptel-model '(o1 o1-preview o1-mini o3-mini o3 o4-mini gpt-5 gpt-5-mini gpt-5-nano))))
     (when (and gptel-temperature (not reasoning-model-p))
       (plist-put prompts-plist :temperature gptel-temperature))
     (when gptel-use-tools