feat: compatible custom avatar url (#26975)

Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>

api/libs/helper.py

@@ -81,6 +81,8 @@ class AvatarUrlField(fields.Raw):
         from models import Account
 
         if isinstance(obj, Account) and obj.avatar is not None:
+            if obj.avatar.startswith(("http://", "https://")):
+                return obj.avatar
             return file_helpers.get_signed_file_url(obj.avatar)
         return None