[Multi-User Part 3]: Separate chat sesssions based on authenticated users (#511)

- Add a data model which allows us to store Conversations with users. This does a minimal lift over the current setup, where the underlying data is stored in a JSON file. This maintains parity with that configuration.
- There does _seem_ to be some regression in chat quality, which is most likely attributable to search results.

This will help us with #275. It should become much easier to maintain multiple Conversations in a given table in the backend now. We will have to do some thinking on the UI.

src/database/models/__init__.py

@@ -82,9 +82,27 @@ class LocalPlaintextConfig(BaseModel):
     user = models.ForeignKey(KhojUser, on_delete=models.CASCADE)
 
 
-class ConversationProcessorConfig(BaseModel):
-    conversation = models.JSONField()
+class OpenAIProcessorConversationConfig(BaseModel):
+    api_key = models.CharField(max_length=200)
+    chat_model = models.CharField(max_length=200)
+    user = models.ForeignKey(KhojUser, on_delete=models.CASCADE)
+
+
+class OfflineChatProcessorConversationConfig(BaseModel):
     enable_offline_chat = models.BooleanField(default=False)
+    chat_model = models.CharField(max_length=200, default="llama-2-7b-chat.ggmlv3.q4_0.bin")
+    user = models.ForeignKey(KhojUser, on_delete=models.CASCADE)
+
+
+class ConversationProcessorConfig(BaseModel):
+    max_prompt_size = models.IntegerField(default=None, null=True, blank=True)
+    tokenizer = models.CharField(max_length=200, default=None, null=True, blank=True)
+    user = models.ForeignKey(KhojUser, on_delete=models.CASCADE)
+
+
+class Conversation(BaseModel):
+    user = models.ForeignKey(KhojUser, on_delete=models.CASCADE)
+    conversation_log = models.JSONField(default=dict)
 
 
 class Embeddings(BaseModel):