Default to gpt-4o-mini instead of gpt-3.5-turbo in tests, func args

GPT-4o-mini is cheaper, smarter and can hold more context than
GPT-3.5-turbo. In production, we also default to gpt-4o-mini, so makes
sense to upgrade defaults and tests to work with it

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

@@ -112,7 +112,7 @@ def converse(
     user_query,
     online_results: Optional[Dict[str, Dict]] = None,
     conversation_log={},
-    model: str = "gpt-3.5-turbo",
+    model: str = "gpt-4o-mini",
     api_key: Optional[str] = None,
     api_base_url: Optional[str] = None,
     temperature: float = 0.2,

src/khoj/processor/conversation/utils.py

@@ -23,6 +23,7 @@ model_to_prompt_size = {
     "gpt-3.5-turbo-0125": 12000,
     "gpt-4-0125-preview": 20000,
     "gpt-4-turbo-preview": 20000,
+    "gpt-4o-mini": 20000,
     "TheBloke/Mistral-7B-Instruct-v0.2-GGUF": 3500,
     "NousResearch/Hermes-2-Pro-Mistral-7B-GGUF": 3500,
     "bartowski/Meta-Llama-3.1-8B-Instruct-GGUF": 20000,
@@ -136,7 +137,7 @@ def generate_chatml_messages_with_context(
     user_message,
     system_message=None,
     conversation_log={},
-    model_name="gpt-3.5-turbo",
+    model_name="gpt-4o-mini",
     loaded_model: Optional[Llama] = None,
     max_prompt_size=None,
     tokenizer_name=None,

src/khoj/utils/rawconfig.py

@@ -89,7 +89,7 @@ class SearchConfig(ConfigBase):
 
 class OpenAIProcessorConfig(ConfigBase):
     api_key: str
-    chat_model: Optional[str] = "gpt-3.5-turbo"
+    chat_model: Optional[str] = "gpt-4o-mini"
 
 
 class OfflineChatProcessorConfig(ConfigBase):