Fix: add avatar for UI (#11080)

### What problem does this PR solve?

Add avatar for admin UI.

### Type of change

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

api/db/services/canvas_service.py

@@ -67,6 +67,7 @@ class UserCanvasService(CommonService):
         # will get all permitted agents, be cautious
         fields = [
             cls.model.id,
+            cls.model.avatar,
             cls.model.title,
             cls.model.permission,
             cls.model.canvas_type,

api/db/services/knowledgebase_service.py

@@ -201,6 +201,7 @@ class KnowledgebaseService(CommonService):
         # will get all permitted kb, be cautious.
         fields = [
             cls.model.name,
+            cls.model.avatar,
             cls.model.language,
             cls.model.permission,
             cls.model.doc_num,