Add API for additional user attributes
Reason for Closing:
Reason for Blocked:
Support Suite Ticket:
We need API call ```user.set_attribute` [user_id, key, val]``` to handle user notes and others, like save user theme.
feat(middlewared/account): add `user.set_attribute` This way a client can set general purpose attribute keys without having to worry about preserving other keys with `user.update`. Ticket: #27608