Default to gpt-4-turbo-preview for chat model, extract questions actor

GPT-4 is more expensive and generally less capable than gpt-4-turbo-preview

src/khoj/processor/conversation/openai/gpt.py

@@ -19,7 +19,7 @@ logger = logging.getLogger(__name__)
 
 def extract_questions(
     text,
-    model: Optional[str] = "gpt-4",
+    model: Optional[str] = "gpt-4-turbo-preview",
     conversation_log={},
     api_key=None,
     temperature=0,

src/khoj/utils/constants.py

@@ -7,7 +7,7 @@ app_env_filepath = "~/.khoj/env"
 telemetry_server = "https://khoj.beta.haletic.com/v1/telemetry"
 content_directory = "~/.khoj/content/"
 default_offline_chat_model = "mistral-7b-instruct-v0.1.Q4_0.gguf"
-default_online_chat_model = "gpt-4"
+default_online_chat_model = "gpt-4-turbo-preview"
 
 empty_config = {
     "search-type": {