Support Ollama (#261)

### What problem does this PR solve?

Issue link:#221

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

api/apps/conversation_app.py

@@ -126,7 +126,7 @@ def message_fit_in(msg, max_length=4000):
     if c < max_length:
         return c, msg
 
-    msg_ = [m for m in msg[:-1] if m.role == "system"]
+    msg_ = [m for m in msg[:-1] if m["role"] == "system"]
     msg_.append(msg[-1])
     msg = msg_
     c = count()