Comment 2 for bug 1778949

The new proposal seems reasonable. We have a similar feature in oslo.config with the DeprecatedOpt class: https://github.com/openstack/oslo.config/blob/9c71b0140931b51ffffc3bbdc1b655fdaccce45b/oslo_config/cfg.py#L1223

However, I'm not sure in that case if you can set things like deprecated_reason on the DeprecatedOpt or if you still have to set it on the main opt. In any case, this does seem like a better way to do it.